I'm not an expert but I think its just personal choice based on what tracks have been done, how many of them are remixes and how many or new tracks. So most punters would expect 2 tracks and maybe one or two remixes in an EP lasting 18-20 minutes in total if you're paying 5 quid and maybe postage. Tell you the truth I'm glad for a couple of remixes on a 12" because its often the b-sides that really pound and clank and make my heart bump! So in my mind as many as you think will attract people to buy it. I've got some killer tracks that are only single sided vinyl and I love 'emand would pay more for them than some albums I've got.

Anyway as I said I ain't an expert :)