[Gogar]

I suggest you oversize the conduit in case you change your mind about wire size. No one ever looked back and wanted the conduit smaller.

except 105' is a long pull so you will most likely want to pull the wire as you assemble the conduit, and then bury the whole thing. actually pulling 100 feet would suck.

Remember you need to pull a green ground also to the main panel and you still need to physically ground the sub panel at the outbuilding.

Absolutely run a conduit with 2 cat6 unless you don't wanna buy that extra conduit you can get direct-bury cat6.