I like magic-heavy parties. My normal starting character is either a necro or a priest. So out of the starting line-up, I swap my hireling necro or priest for Ithilgore, and the knight for Cauri Blackthorne. The rest I leave as they are.But you're right IMO to stick with close to the starting line-up. I once played a game in a manner which allowed me to hire the level 50 hirelings as early as I could, and didn't enjoy it. I found I missed out almost entirely on the kick you get from successful character development, and the game was so easy with those characters that it became boring and I never actually finished it.
I have done it twice with one of Ice3's dragon starting characters, and in those cases I just swapped Simon for Cauri.
