This has probably been said, but, setting aside excessive powergaming, and any use of suplements...
MerakSpielman said:
AC: If he's going to mingle in melee, he'll need a good AC. If he's going to cast arcane magic, he needs no armor check penalties.
Arcane spell failure is an issue, but, there are spells that take no Somatic components, including the one you're specificly looking at: True Strike. Blur is another, and it'll help keep you from getting hit.
If you go with a high DEX, you'll be able to wear lighter armor while retaining a decent AC, giving you a lower arcane spell failure %. Combined with careful spell choice (pick combat spells with no somatic components, and non-combat or long durration spells that you can cast before donning your armor) that can be enough. Or, you can eschew armor in favor of magical protection... if the campaign you're in is 'high magic' (bracers of armor and the like readily available), that might be a good option.
I'm thinking of maxing out CON (putting highest score there and increasing it every 4th level) and leaving STR low (for the true strike/power attack combo to compinsate for).
I think that's a sound idea. You probably don't want your STR /really/ low, you need a 13 for Power Attack.
CHA: He also isn't targeting the enemy much if at all, so has no need of high DCs. How much CHA does he need?
At least 10+the highest level spell you ever intend for him to cast (if you're only ever going to be 7th level Sorcerer, 13 would be adequate), and no more than 10+2*spell level (if you want to get a bonus spell of the highest level he can cast). If you're never going to get more than 5 sorcerer levels (2nd level spells) a mere 14 CHA will give you a bonus spell of each level.
Should he only buff up if he knows a fight is about to break out?
There are both long- and short- durration buffs. You should pre-cast Bull's Strength or the like if you /suspect/ there will likely be a fight within the hour. You should cast Blur right before combat. Only things like True Strike should be cast in the midst of combat. If you ever get to 6th level as a Sorcerer, /Haste/ will be very handy to address this issue.
I'm thinking instead of Ftr/Soc he might go for Brb/Soc for the extra HP and rage.
Depends on how many feat chains you're interested in. If you don't want much beyond Power Attack, and raging fits your concept, Barbarian may be the way to go. The Barbarian's in-class Intimidation combined with the Sorcerer's CHA, could be nice. Uncanny Dodge would help you retain your AC when surprised. And, 'instinctive' spellcasting wouldn't clash with a 'barbaric' background.
OTOH, if you picture a clever fighter with many tricks up his sleave, a Wizard might be better than Sorcerer... fewer spells/day, but you get the new levels earlier, and the 13+ INT means more skills and that you qualify for Expertise, which could help your AC, especially on rounds when you do the True Strike/Power Attack combo (according to the Sage, you can max out both, IIRC). Wizard would also allow you to vary you spell selection more, when you know what you'll be facing... for instance, memorizing all non-Somatic or Stilled spells when you're planning on combat, vs non-combat/Somatic spells when you don't forsee the need to don your armor that day.
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In any case, as a melee-oriented caster, you will want to absolutely max out your concentration. Interestingly, Paladins and Rangers have that skill in-class, so there might be another option, there. A Paladin/Sorcerer would get a lot of milage out of his CHA, for isntance, and a Ranger/Wiz would benefit greatly from high INT (for skills as well as spells.
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Finally, consider saving throws. You will have a much better WILL save than the average fighter. If you don't make your magic use excessively obvious, enemies may occasssionally 'waste' WILL-save attacks on you. Your REF save might not even be that bad, as a high DEX is clearly desireable (to avoid the neccessity of heavy armor).
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