You've gotten good advice from everyone but I think that if it was me, I'd buy new hub assemblies and bearings. If the the trailer has been sitting idle as you say, and you're going to be doing any trailering at all, I'd play it safe and change the hubs and bearings. They're not expensive and the peace of mind on the highway will be worth it.
I'm fixin' to mount my spare on a hub assembly as well. It might sound extreme but, that's what I'd do.