[Celacena]

Yoshimo is unavailable in ToB.

I found that my FMT was really a F/T with added arcane skills. the levelling takes time, but using the Deck of Many Things whilst other party members take time off really boosts levels if you somehow get THRONE as your final draw (see DoMT info on this site).

If you have Jan, have the PC get their stealth and set traps high and leave finding/unlocking to Jan. Knock spells are only level 2 though...

for a neutral PC, I would go with Keldorn (despite his alignment), Sarevok, Jan and Viconia/Jaheira. K's true sight and dispel are very very useful in ToB and having him and Sarevok as 2 tanks saves the PC needing to get stuck in quite as much. there are times when enemies will use death magic or otherwise seem to have vorpal-type attacks and you don't want to be re-loading more than you need.
Viconia is a very effective cleric and doesn't cause the aggro that she does in BG2. at high levels she 'turned' Keldorn! took me by surprise that one!

so the core should be a tank, a caster and a healer - if the PC gets enough thief skill points, then you can go with Edwin as caster instead of Jan.

I recently emptied out the Arcana archives and that gives a caster a LOT of scrolls. However - multi-class characters find it difficult to get to level 9 spells and you need to balance the xp of learning them against putting the scroll in the quick slot and having a PI/Simulcrum cast instead.

(that reminds me that with Vailor's Helm, a cleric can void the tiredness of casting restoration)