OK, I just did a brief dry run drafting a team under this criteria. My starting five was at about $22 mill, leaving me with $10 million for a 7 man bench. I think that is just about right, dont you? With the extra money, everyone should be able to save enough money so their last couple scrubs make the usage limit (as jcred points out). If not, you will have to modify your starters with lower salaries so that EACH of your bench players have a high enough usage rating.
And yes, EVERY SINGLE PLAYER on your team has to be below 30 D and above 20 usage. You will be AMAZED how many defensive slacker cherry pickers there have been in this game.
I am giddy with the idea to see how you guys draft in this league. The standard "Get two 30+ rated 3 pt shooters and two dominant rebounders that leads to success in most leagues will be seriously tested in a league like this. Sure, you can find guys like that here, but THESE guys who do that at these salaries are so one dimensional, they may hurt you more than help.
Either way, drafting a team for this idea will probably be COMPLETELY different than in most other leagues.