ArbitraryWater: In general, you should probably pick your team and stick with it throughout the game, though some of the level 50 characters are insanely good and don't require the training that your regular party members require. In fact, if you want the game to be anything resembling a challenge, don't recruit any characters that are above level 5. There are some pretty powerful characters who make the earlygame a joke if you know where to find them.
In particular, if you are willing to dodge some basilisks in the Murmurwoods, you can recruit the level 50 Dark Elf Patriarch, who has all the elemental spells up to master level and can be obtained immediately upon reaching Ravenshore. And of course, even disregarding that there are the always ubiquitous Dragon characters, all of whom break the game.
The game is still much easier than VI and VII regardless though. It just depends on how early you want your team to turn into a bunch of steamrollers
no need to doge if you get the lvl5 dragon from garrot gorge, train him a couple of levels, get master in dragon ability and then fly over murmurwoods :P