I don't really remember if the plans allow you to convert to bolts at a later time, but I'd suggest going with the bolt on method from the start. Rubber bands are a pain and they mess up the covering after a while.

One other piece of advise, build the "sport" wing with less dihedral. I built one last summer for my dad and I built the "trainer" wing and there is too much dihedral IMO. A 10mph crosswind will blow it right over.

Ben