You really need 6 characters in this game. Unlike Wizardry where the experience is divided up, in this game having more party members won't make a difference there.Reading the Basic Guide is well, quite useful. You can also shell a few buck for the Tactical Guide which is also very useful.
Don't be afraid to put up two Ogre Fighters up front at the beginning, they will be your meat shields, consider them as expendable characters that you will replace eventually, it doesn't matter if they die a lot in the beginning, the idea is to get 2 or 3 "main" characters going first.
Snafaru