Suggested level aside, should I do them before or after I finish the main quest?

Bloodmoon is pretty much independent, but the Tribunal has a few elements from the Morrowind main quest. Almalexia will spoil some things about the main quest line, if you aren't halfway in that one. So, yeah, Morrowind --> Tribunal, and bloodmoon fits everywhere.

I'd agree with the post above. Bloodmoon is an entire quest and landmass all to itself. Tribunal 'follows on' a bit more and you might find you don't want to go back.