Thanks Nick and Mark.
Mark - I use midi via BFD module (they have some great kit sounds and all velocity sensitive and you're able to mix different kit parts. It also allows for human time keeping i.e. not perfect). What I normally do is 4 bars at a time. It's the usual set up - kick will be on C0 and snares are on C#1, D, D# and so on. I normally set it on a 4 bar loop and start to compose/record a basic rhythm until I have the structure to my song. I will then go back and fine tune and add the accents, fills and try to make it as convincing as I can (remembering that a real drummer would be better but that's another matter) It really depends on how much time you want to put into your song.
Billy.