| Alci |
Well here's my 2 cents about a Str Magus build.
With a 20 Pt build as an Elf i'd go this without dropping stats.
Str(16) Dex(12+2) Con (13-2) Int (14+2) Wis (10) Cha (10)
No idea at what Lv your starting out, so I'll assume its Lv1.
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A Str Magus wont have to burn a feat for weapon finesse(dex to hit) and a feat for (dex to dmg) -Dervish dance(3 perform included)-
(Note: Also heard somewhere that slashing grace or fencing grace does not work with spell combat but maybe your DM houseruled it.)
Also since your an elf, i assume you haven't known about the Elven Thornblade as a replacement for a rapier. Its a one handed elf martial slashing or piercing weapon as long as your char has weapon familiarity. 1d6 18-20/2x S or P and +2 Atk roll for crit confirms.
Another reason for going Str depends on the campaign, if you were to lose your equipment and left with a wooden club for example, you wont be too helpless.
A Chain Shirt or Leather Lamellar (4 Armor AC) and Shield spell (4 Shield AC) should be good enough starting out. Sure you lose 2 dex ac, 2 reflex and 2 initiative in comparison but that's where your later Debuff spells, Curse spells, Hexes, Buffs like Haste/Blur/Displacement/Mirror Image comes in.
Now about armor penalty.
It affects your fly skill a little bit but not too much, unless your in a severe wind speed area. By Lv6 with Flight Hex, assuming you grab it at Lv6, remember that Fly spell from hex gives you 1/2 Caster lv bonus(+3 fly bonus assuming Lv6), as well as good flight (+4 fly bonus). As long as you have like 15 on fly checks, you wont have to roll doing any flying except 180 degree turn in normal conditions.
Acrobatics, well instead of rushing past enemies if you don't need to move safely and hex them while letting your frontline deal with them. As well as Spellstrike them.
Stealth, I hope your party has a rogue for that, if not then have invisibility-like spells ready.
Escape Artist, one way to escape from a grapple, and if any knowledge check told you about the enemy's saving throws & immunities. Use that supernatural ability hex like Slumber to sleep them, and hopefully evileye'd their saving throws.
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As a hexcrafter magus, i'd recommend a higher int mod for higher dc against your hex and spell effect saves.
Slumber for that Sleep Lv=turns or Evil eye for the 3+IntMod turns of debuff if succeeds. If you want better chances to succeed debuffing, you'd need int. Debuffs can help your allies to change the tide of battle.
Flight is good for early Flying & emergency falling. Healing hex is nice for the extra one heal per person, or the downtime community service of healing others. Misfortune is good if they fail their save.
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Feats
Depending if your the only caster or DM allows crafting, consider craft magic item feats to help the party getting gear at discounted gold.
If your crit heavy, maybe consider the Eldritch Assault feat line. Allows crit to proc on threat once per round as long as you have some sort of concealment against enemy.
Also Kurald Galain has some nice tips on magus here
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As a magus with your archetypes, to be honest, its not wise to jump into the flay off the bat. Remember use shield and/or flight before a fight if possible. Best identify the enemy info with your skill in knowledge and spellcraft first, then consider your options.
Running at a Huge creature without buffs up or debuffs down is near suicidal. Surviving a fight is more important.