I could use a little help in development here.

[Setorines]

Alright, I intend to start DMing here in a few weeks, but I don't plan to play straight pathfinder. I have a few changes to the game that I want to implement but need some help doing so. The main change being that my world has no magic except that which is provided by the gods.

When it comes to character selection i know this will limit my players can chose and some will be tempted to become a monk or paladin and while I won't outright tell them they can't i will advise against it.

Now that there's no magic in the world (for the most part) at the end of my first major quest i will introduce "gems" to my players each getting 2. These allow any character to do magic, but only specific spells which are a part of the gem, and instead of having a limit per day they will cost the health of the player.

Here's a list of the gems and a simple explanation of each:

Fire: allows the user to create and control fire.
Water: Allows the user to control, locate, and freeze water.
Earth: allows the user to control the earth beneath their feet, and the wildlife/plants around them.
Air: allows the user to control and purify the air around them. Even to a molecular level.
Electricity: allows the user to create electrical surges and control the lightning during a thunderstorm.
Telekinesis: allows user to control small objects near them. (Launching as a projectile is still relatively complicated and I may scrap the idea of this one all together combining it with the next and finding a replacement.)
Telepathy: allows user to be able to read minds, and feelings as well as pushing their own emotions onto others. (Such as confidence to an ally to give them a boost, or fear to an enemy)
Buff: i originally had 12 gems but decided to put a few of them together all into this gem.

Just before the buff gem was made i came up with the concept of leveling up the gems, and adding an additional called gem mastery to roll for in character creation. To give you an idea of what I mean ill show you the buff gem which is done up to level 5 and the fire gem which i only have the first 3 spells for.

Buff gem

Strength- acquired at level 1
Gives the user great strength.
Cast time: 1full turn
Effect: Strength mod x 2
Duration: 1d8*gem level (minimum of 6, maximum of 24)
Range: self
Backlash: 1d10-fort-gem mastery

Intuition- acquired at level 2
Gives a great increase to all knowledges and crafting in the game. This effect can be used during combat to effectively dodge and land attacks as well.
Cast time: 1 full turn
Effect:Using this gems gives a +10 to knowledges, crafting, AC and your to hit roll.
Duration: 1d8*gem level (minimum of 6, maximum of 24
Range: self
Backlash 1d10-fort-gem mastery

Healing- acquired at level 3
Allows you to give your health to help an ally.
Cast time 1 standard action
Effect: heals an ally for 1d8+gem level
Duration: instant
Range 30 ft.
Backlash: 1d10-will-gem mastery

Speed-acquired at level 4
Gives the user great speed
Cast time: 1full turn
Effect: grants all actions during the battle phase twice
Duration: 1d8*gem level (minimum of 6, maximum of 24)
Range: self
Backlash: 1d10-fort-gem mastery

Accuracy- acquired at level 5
Increases your chance for critical hits drastically.
Cast time: 1full turn
Effect: adds a +5 bonus to your to hit roll, and still treats it as your natural roll.
Duration: 1d8*gem level (minimum of 6, maximum of 24)
Range: self
Backlash: 1d10-fort-gem mastery

Fire gem

Fireball: acquired at level 1.
You create a ball of fire that fits into the palm of your hand that can then be thrown at your opponent.
1 standard action
Damage: 1d10+gem level
Range: 60ft.
Backlash: 1d10-fortitude-gem mastery

Flamethrower: acquired at level 2
You shoot a blast of fire directly ahead
1 standard action.
Damage: 1d4+gem level

Cone of fire: acquired at level 3.
Expands the flamethrower to allow it to cover more ground.
1 standard action.
1d4 per gem level to everyone in the damage area.
Range 15 ft.
Backlash: 1d3 per gem level-gem mastery

First of all i would like to ask if you think the concept of unlimited casting at a cost of health can work, and secondly I need some ideas of how to scale the spells so they are useful throughout, without being overpowered right away, and make the health drain for using the spell not instantly kill an early level, but not be a loss of like 1 health in later levels. (But still easier to cast as time goes on.)

Sorry for not having spoilers to make this easier to keep up with. First time posting, and posting from ipad.

[Kyoni]

No magic means there are no arcane spellcasters at all? and no divine casters too?
Or just no magic items?

If this is your first time DMing, I heavily advise against any houserules, especially such drastic ones, that change the entire game balance.
You need to get a decent understanding of the balances and mechanics before tinkering with them. And this is not something DMs can describe to you on a forum... it's something you need to know from experience.

If this is not your first time:

Make a list of available classes, don't go "you could, I advise against it".

What's wrong with paladins and monks when magical classes are not available? because otherwise there's fighter/barbarian/rogue/ranger?

Also, how do you intend to handle the healing? Be aware that spellcasting draining HP means somebody patching people back together. Without magic?

What's stopping some PC to hand his gems to another PC because he doesn't want spells? What will be the consequences?

Honestly all of this sounds like too big a change... I seriously advise against it. I fear this will end with a martial-centric group who'll just ignore spells altogether as in a no-magic world enemies shouldn't have access to magic either.

[Mark Hoover]

If you're saying no to something in your game, say no. Also restrain yourself from saying "you players get no magic..." and then outfitting your NPCs with magic. That being said, your gems sound cool. If someone has 2 of them, can they combine them for interesting effects?

Fire + Healing to give the effect of Infernal Healing or Regeneration or something?

Also unlimited casting/health: I say take a look at the old Dark Sun game. They had something similar. Also there's Runequest where everyone had a stat called Power. This stat (and supporting storage battery items) were the reservoir casters could dip into to cast spells.

Frankly I think that's more reasonable. If all spells are divine, they're powered by Wisdom. Everyone has a number of Power points = to their Level and Wis mod. Once these are evaporated, the caster can keep casting, but they take Wis damage and risk permanent madness.

Then give every gem a set amount of spells, and have these spells require Power = to level or something. If you find a gem of Wish, you can have unlimited wishes, but each one drains say 9 Power. If you're a 20th level fighter focused on Wisdom, you can have say 3 wishes in the day and take 1 pt of Wis damage, but you'd be ok. However if you're a 1st level commoner you'd use this gem once and go brain dead.

[Anguish]

I get the impression that you've got this neat idea for gem-magic that anyone can use and you're removing traditional magic so that gem-gamic shines. I might suggest (as Kyoni) that you not make such sweeping changes to the system your first time out. Instead, let you players know that you want to experiment with a tacked-on system that may or may not need some balance changes after launch.

Let your players play whatever they want. Traditional wizards, clerics, whatever. But those who decide they want to play straight martials like fighters or barbarians know that there's this interesting gem-magic thing that they can dabble in.

Test your new idea but keep the fundamental game intact so you know if your system is even vaguely balanced. Once you build such a system, then you could reasonably consider relying on it.

Just my thoughts.

[Setorines]

Hey sorry i have replied to this one, i accidently double posted this and was looking at the other one.

As far as why monks etc. would be allowed all magic would come from the gods and only from the gods. Anyone that can have magic wouldn't accept the gems being as their power would come from a god other than their own,

The idea of combining gems would be very interesting and I may incorporate it later, but Itheres a lot on my plate already as it is. I'll let my players know in advance that tweets are bound to happen, and if the health drain of a spell is too much, or they feel the gem is too OP in comparison to the others then I'll change it.

And since I posted this i came up with the idea of a mana pool thats based off of a new attribute all together that I'll call gem mastery. You can go past the amount of mana you have, but then it starts cutting into your health.