For certain parts and quests you'll definitely need 4 prople so don't wait until the stronghold. You can't respec them completely but depending on when you pick them up you'll have a lot of freedom nonetheless. For instance yesterday I finally talked to the woman in the cage in Cyseal while my characters are level 10. She had some catching up to do when I picked her up and I got to fill in all the points she had missed in comparison to my other characters. Depending on th difference in the level it can make a major difference or not. Starting specs will remain the same however.
My tip, pick up Jahan if you can. He's an amazing sorcerer even if he is a bit of a weirdo. I think I found him at the pub but not entirely sure.