RE: EVO 90 2007
Unfortunately I haven't used the 90 yet, but I still think a good starter would be to go for the rear strap plugs for the back strap and then choose front strap plusg according to the stance you prefer. The EVO stance is generally quite wide, so do be afraid to "streth out" a bit more than ususal. I personally use the rear plugs back and middle plugs forward on my other EVOs and also on the 06 E91 I used to have. I think most people actually end up with something like that.
As for fins, the supplied 24cm Drake Natural works fine for the smaller sails in the spectrum for pretty much all riders, but I think most will want to go for something bigger for the larger sails. A good complement would be the Drake Natural 26. If you want to tune the board for more B6J style sailing you can use the 26 also with smaller sails (5.3, 5.0 etc) and then you might want to get a more powerful fin for sails around 6.0 and up. In the Drake lineup the new Crossover fin (original equipment on Kombat and (in much smaller size) also on the Flare. Its a Curtis designed fin which is still kind of raked bit with less sweep and its also MUCH stiffer. A crossover 26 could complement the original 24 for a two fin setup and for a three fin setup the Crossover 28 could even be an option (complementing the 24 and 26 Drake Natural). For more specific advice on fins I would need to know what kind of riding you will do on the board and in what sail ranges (B&J, onshore wave, sidewhore wave, big/small waves, riding/jumping emphasis etc).