Such games are perfect for tailoring to the players' tastes, because you only have one player to worry about. And yes, the problem is that several minds can come out with a solution to a problem much more easily than a single one.
Exactly. I have been involved in a couple such campaigns on both sides of the arrangement, and it's a lot of fun for both especially if the DM caters to the kind of game the player wants to play (always true, but much harder with more people). the specifics depend entirely on what kind of game it is. Lots of political/murder mystery style intrigue? Dungeon crawling? Hash it out between player and DM and have fun. Again, it depends a lot on what you're doing, but rogues/bards do really well just for all the versatility.