Consider talking with one of the other players and ask them if they could pick up UMD. It will give you access to a lot of magic via scrolls and wands that you may be missing. The paladin or warpriest are possible candidates for the pick up, and they could get a small bonus to the skill and access to it as a class bonus.
Since your part doesn't have ANY full progression spellcasters, you may need to buy more scrolls than other parties. On the upside, 3 of your party can cast the basic divine spells.
I haven't read through the first mod yet, but that sounds like a really good start for an Eberron conversion.
Orcs to drow tribes sounds like a really great idea.
I would make any items crafted from dragonshards use Siberys shards. Xendrik is one of the primary sources for them, and locals to the region would have easier access to them.
I would make the town of Trunau a suburb or satellite town of Stormreach: as more and more people arrive in Xendrik and stay there, they all can't live in Stormreach, and smaller settlements would start growing up deeper and deeper in the jungle to server as better jumping off points for expeditions.
Are you going to allow players to use eberron specific materials? What are your plans for dragonmark or artificer mechanics for players?
I've been running Rise of the Runelords for a party of 4. There is no way the party would every survive specific encounters without consumables. If a character can't survive fights, they can't live to spend their cash. By spending a little bit of gold to be prepared 'just in case', they can make fights swing in their favor.
Level 1 scrolls, wands and potions are dirt cheap in the long run of things. Loot ends up getting put into a pile and then divided among the party; a lot of that is liquid cash that can be spent on party items like a wand of cure light wounds or resurrections should the need arise.
I encourage my players to pick up universally beneficial items that will be helpful down the road: cold iron arrows or silver daggers for enemies with damage reduction, scrolls of disguise self, obscuring mist or remove paralysis. These things cost very little gold, but can swing the tide of lower level fights in the favor of the players. Everyone should carry an extra potion on their body so an ally can force feed it to them if they go down during a fight.
An obscuring mist cloud gave them the chance to lay down cover during a fight against archers and spellcasters, and stall out for several turns. They have a couple of remove paralysis scrolls in case they encounter nasty ghouls during some encounters.
Consumables provide a way for the players to cover their bases against 'obscure' enemies with minimal investment. They become even more worthwhile when a party member has UMD and can inherit lower level wands from the primary spellcasters, or can use them when a caster goes down during a fight.
Every time someone fires a bullet, they're basically firing 11g at the enemy. Since APs presume a party of 4 or 5, there is a finite amount of gold that exists within the AP that the players can find. Unless the gunslinger goes out of their way to get a caster to use the Abundant Ammo spell, they're burning a lot of money each combat to play their character.
I normally don't have PCs track their arrows, bolts or sling bullets because the cost is ineligible, and its not very heroic; but any gun-user, I'd require to track and acquire their bullets / powder in game. Even more so if they're using alchemical cartrigates.
There is a literal gold cost to playing this kind of character on the low-end of the character progression track, and both the GM and player need to enforce this when dealing with 'emergent / early firearms' setting rules.
I would favor your reading of the rules, they can have access to cure spells and the like, but retain the previous immunities.
In the end, you are the GM and the players should respect your ruling. At the same time though, if the players find evidence on the forums or other sources, you should consider them and feel free to revise your ruling.
Did you document any of your changes to the modules as a GM? What pathfinder conversions are you using for the races, dragonmarks and artificer?
Have you read through all of the modules in the adventure path before re-theming it into Eberron?
I've been putting some thought into how I would frame the adventure as a GM for Eberron, but I'm in the middle of running Rise of the Runelords. I've read through the players guide, and have the first two modules on my bookshelf.
The forum ate my post! D:
I came up with a cheap solution taking advantage of my large table: the chessex mega battlemat + translucent plastic dropcloth. Take standard wet erase markers, cut out enough dropcloth for each layer of a dungeon, and prep your for that whole chapter. I use printer paper or binder paper as a psuedo-fog of war and remove pieces or slightly rearrange them as the players discover more parts of the dungeon.
I like this method because I can see the squares on the map without drawing on the map. There's no break in gameplay to draw maps as players transition from one layer to the next. If a sheet gets too dirty, recycle it and cut a fresh piece. Be careful about orientation though, I've ran into some problems when I've put a map down upsidedown and was slightly confused when referencing the adventure's map.
I would consider using a projector and roll d20, I'm a huge advocate for digital tools, but there's also something old-school and tactile about the grid maps and miniatures on the map. I also hesitate to make modifications to my apartment's walls since I'm still renting.
If your party ever needs xp to help round out their levels before starting a new mod, I would use this NPC to help with that. You could make one or two sessions about hunting her down and bringing her to justice.
I would use the duergar curse a mis-representation of a runewell. Work with the player to settle on some of the details, but I would say when Gretchen was off somewhere, perhaps some pilgrimage, the same surge of power that activated the Sandpoint Runewell, was invoked around the same time, or maybe it was another one feeding off the Catacombs of Wrath well.
I would use the ranger NPC introduced in Burnt Offerings to bring tidings of the NPCs activities to the PCs, and hopefully after concluding that plothook, the inquisitor will remain with the party.
I would create a new NPC that has an association with one of the Lamia's in the end of the Skinsaw Murders or under the influence of the patron running the pleasure barge in the next module for Assault on Hook Mountain.
As the great threats to Sandpoint get revealed, the inquisitor should want to stick around. The early mods are dripping in Lamashtu cults and demon worship, and those are easy hooks to keep the character around. I would also work with the player to establish some sort of personal connection to the region, a source or contact that they've worked with in the past that you can leverage to keep the player around. Either Father Zanthus who heads up the Sandpoint Cathedral, or some other local, maybe the ranger?