Can I turn off DQ in multiplayer, and against Uke in challenge mode, and how do I make matches longer against Uke in challenge and in Free Play?

for longer chalenges while faceing uke go into setup,gamerules and change the game time to what ever you like.
hope that helps.
and no you cant turn of dq in multiplayer unless you create you own room then you go into options and turn off dq.

Actually, DQ is in Game Rules, not Options. Game Rules is in Setup in the main menu as well.

It won't let me set my matches against Uke past 500, is that the maximum?

type /set mf 501. press enter, then esc and freeplay and see if it works.

As for dq, you can always type /set dq 0.