Hey, So I actually own this game on steam, and I am attempting to get all achievments. My next run will be solo and I plan on doing a Fighter/Mage/Thief who wields a katana and a bow. my question is should I focus on dexterity or strength for a katana?

Strength. Melee bonuses (THAC0, damage, bashing) come from Strength, whereas Dexterity confers ranged bonuses, reaction adjustment (who goes first), AC bonuses and thieving bonuses.

I dont think Katana recieves any benefit from a high Dexterity. So max STR would benefit you more. But ofcourse you would do good to make them both 18 for better AC and Thief skills.

thanks guys

Best is maxing both. Dump wis and cha instead.

Dexterity is more important than strength. The +4 bonus to AC for 18 dex will make a difference, the bonus to thieving skills and the +2 to hit with your bow won't hurt. There are far more ways to buff strength than dex in the game.

The only race who can be F/T/M is Elf and they have a +1 to hit with longswords. Since there are more and better longswords in the game than katanas, I'd recommend picking longsword instead.

Stats to aim for:
Str 18/00, Dex 19, Con 17, Int 18, wis and cha are dump stats
And make sure to pick find fimiliar as one of your starting spells and cast it asap for extra hitpoints. (Then put your familiar in your pack to keep him safe)

consider dual wielding instead of using a shield

Actually, I am pretty sure that only Half-Elves can be triple classes, and I believe they don't get that bonus.

Depends. Weimer's Tactics mod adds some awesome katana action. But it does make the game vastly more difficult.

The rest, spot on.

We're both wrong. BG:EE lets both Elves and Half Elves triple class ;-)