im having a hard time figuring out how to set up my group ...
the only character i really like is Yoshimo ,
what about the others ? Mincs .... Korgan .. Aerie ..Jaheira .. Valhala ,, Viconia.... any suggestions ?

Depends on who you are. Remember you need a thief, at least 1.0 healers and 1.5 casters. Nalia, Edwin, and Imoen can be considered 1 caster (Edwin maybe equal to 1.4 casters). Aerie and Jan are equal to 0.5 casters.

Viconia is equal to one healer; Aerie and Jaheria are equal to 0.5 healers, Cernd, Amoen are worth something less than one healer.

You also probably want 2.5 fighters, one of whom can use range weapons.
Minsc, Valygar, Keldorn, Korgan and Mazzy = 1 fighter each (Korgan worth a little more, maybe 1.4 fighters). Jaheria=0.5 fighter.

In chapter 6, I have a party with me (lvl 7? Kensai duelled to mage lvl 14), Jaheria, Minsc, Korgan, Jan, and Imoen. It is doing great so far so I would personally reccomend a setup like that. Korgan is really good with the axe and minsc is great w/2 handed swrd (not to mention funny). Jan is my thief and he can use magic. Jaheria is a tank/healer and can alos summon a bunch. And Imoen, she just sucks but I keep her in because of the plot (she seems kind of important in the plot)

I personally opt for a power group. I have a berserker main character, korgan, mazzy, anomen, jan and minsc. then just trade jan in for imoen and have bases covered.