Fruityloops is good for that sort of stuff (I do alot in 5/4, and experimented in 3/5 a couple of times.... hard but worth it). As for the intervals in a different time signature, you can play with up to about 16 beats before it goes funny. The shuffler is your friend . With it, you can shift ticks and make it seem like you're in a triplet, or what have you all else fails, you can play with the snap tool which can come in very handy inside the piano roll. bleh... I think you're set