Given that the theme is forced alliances which may or may not be balanced, I don't think it's particularly fair to make a large bet for the game. I'd propose a 20-point bet at the most; 200
with WTA would still be a sizable reward and it shouldn't burden anyone who wants to play too much.
As for phase length, I'd prefer 1-2 days. 36 hours would be ideal.
And to clarify my original variation comments: Turkey "switching sides" just means Turkey plays like a normal Diplomacy player would. It's not bound by any team obligations and can basically freelance. While that sounds wonderful, though, be sure not to piss too many people off... the three power blocs are just as likely to see Turkey as a dangerous wildcard and a mutual threat to their alliances' survivals as they are to see it as a potentially valuable ally.