So, I replayed all the level 17 adventures repeatedly for minimal exp to finally make level 20. There's no more advancement as I can't gain any exp. I'm currently replaying all the low level adventures.. which are also unbelievably easy since my selection of gear requiring no talents is substantially better than when I first started. (Fiery Stab on a 6hp kobold anyone?) I will say, all these low level adventures generate a lot of gold really quickly. Takes no time to finish them and you get the same gold for some crappy common level 1 weapon as you do for a level 16 one which required way more effort.
What Wozarg said. Challenges give more loot than normal. Also BlueManchu are with holding content at the moment till they make the game more stable and ensure complete playability of the game and any aditional major changes before more stuff to do. Alternatively you can do multiplayer and try to beat Jon's current record.
I would suggest doing no party death challenges on each adventure first. Then moving onto 'all same class/race', next would be drawback
Well, you can always: 1. Farm for 3 of each interesting items, in case you ever want to do a party of all x class with the same setup. 2. Level up more characters so you can have any combination of party available. (That's 3 characters for clone party, 3 class, 3 race = 27 characters)
On that topic I would have to say that from the impression I've got so far you could literally try any combination and be successful with it - hardest would be a triple elven wizard, at least early game... but it would be really interesting to see
You could always lend your account to people that haven't gotten a chance to play yet! I'm not asking for myself, since I'm already in (and nowhere near as advanced in the game as you, lol), but there are plenty of people still waiting to play.