thank you all for the answers
who should I take the leadership and blacksmithing with btw? (party of 1 mage, 1 melee rogue, jahan and cain (madera))
also combination of 2 mages (heavy pyro/2 orso geo/2 hydro/2 witchraft) + Jahan (heavy hydro/heavy air/1-2 pyro/2 witchraft) or something like that?
Since Jahan starts with Scientist, you might as well have him take blacksmithing. Note that you never need to put more than 2 points into blacksmithing or crafting with Jahan. You can find or buy bracers and belts that give +crafting/blacksmith fairly easily; this together with Scientist means you have an easy +3 bonus to both on Jahan.
As for leadership, it depends. The bonuses on leadership are: +initiative, +damage, +chance to hit (level 3+), +crit chance (level 4+), +willpower (level 5+), +immune to fear (level 5+), +bodybuilding (level 6+). I think the bonuses are more powerful on warriors/rogues/rangers than on mages, so it may make more sense to take leadership on one of your mages since the person with the leadership ability doesn't apply the bonuses to himself.
Another thing to consider is that leadership gives +5 initiative, which turns into a whopping +10 at level 4+. It is really hard to match that bonus without pumping lots of points into perception/speed. This means that whoever has the leadership ability probably will be taking their combat turns after all your other party members.
Finally, you can find the +leadership stat on helms (in my experience more common on str-based helms than dex-based helms, but don't take this as gospel) and weapons. Just something to think about if you like to min-max.
