Is your SIL in Tuscon too? Where is your family?
Don't invite people you actually aren't friends with. As far as your friends go - could you have the shower there instead? Could your SIL swing that? it would be easier for you- one person- to go to where the majority of people are.
But again- where is your family?
However, I also agree- it's WAY too early to seriously be talking about a shower. Nothing wrong, though, w/ getting some ideas together - especially on location.