Ok, this is a tricky build. The multiclass is rather mismatched.
Not being able to use armor (since you are going sorcerer) is one of the things to consider when assigning scores. You already have two scores that are higher priority than DEX (CHA and STR) so I say just don't worry about AC and concentrate on STR, CHA and CON.
Let's look at the races that give you a bonus to those two.
Angel-Blooded Aasimar gives you a bonus to those two and no penalties (you will probably have to check with your DM to pick it, though). Plus, bonus points for having both angelic and fiendish ancestors!
Demon-Spawned Tiefling also gives you a bonus to those two, but you a take a somewhat not that important -2 penalty to Intelligence (Tieflings require you to take a feat to choose the different bloodline, which is rather unfair. Talk to your DM and see if you can wave that).
Humans can replace their bonus feat and their additional skill point per level to receive an additional +2 to another ability score... but that's basically all you would get from that race.
Sulis and Nagaji both also give you a +2 STR and CHA bonus with a -2 penalty on INT. Sulis have a most awesome Resistance 5 to cold, electricity, acid and Fire, so they are probably the best choice.
If your DM doesn't allow ANY of the above choices (Say, if you are playing only core), then any race that grants you a bonus to STR or CHA and doesn't give you a penalty to other (or CON) is good enough.
With a 20 point-buy (and assuming +2 to STR and CHA and no penalty to any stat), this is what I would build:
STR- 16+2
DEX- 10
CON- 14
INT- 10
WIS- 10
CHA- 14+2
If you are taking a -2 penalty to INT, consider lowering your WIS to 8 and upping your INT to 12, so that you don’t get a not-at-all desirable (from a roleplaying perspective, at least to most players) negative INT modifier.
If your first level is Barbarian, then you have a bunch of HP to begin with and offset your low AC somewhat. I would also take Barbarian as my second level, giving you a larger HP cushion, increased BAB, more Rage rounds and (most importantly) a Rage power. Said Power could be reckless abandon. It will lower your AC even more, but at this point your score is so low that it is more or less the same, and will allow you to have a more competitive attack bonus.
All the other levels should be Sorcerer levels. You are already quite behind on your spellcasting capabilities, but on the other hand, you are a melee powerhouse. My advice is to concentrate on Buffs and utility spells.
If the campaign uses traits, then there is one that gives you a +2 to your caster level, as long as it doesn't exceed your total Hit Dice (I keep forgetting it's name, so you'll have to look it up). There are some other good traits, but few of them exceed the one that gives you a +2 bonus to your initiative.
As for the feats... well, there are a ton of viable options. Weapon Focus is good for hitting your foes, something that you will be doing quite often. Toughness further increases your HP, something you'll need with your low AC. Metamagic feats can wait until the higher levels.
So, there you go, hope it helps!
