I'm doing my first wedding cake in early August and I'd like to make the cakes in advance so I'm not overwhelmed at the last minute. Two questions:
1. What's the longest I can freeze them without risking the cakes getting soggy?
2. Is it ever ok to freeze a cake with buttercream already on it or will that create water droplets?
Thanks, experts!

I would only freeze something for about 2 weeks. I don't know if it can go longer, but that's my best experience, personally.

You can freeze with buttercream already on. Take it out the night before you need to decorate and let it thaw. Make sure the surface is dry and free of condensation before you put your final coat of buttercream or fondant on, because you don't want bubbles!

...first wedding cake in early August and I'd like to make the cakes in advance so I'm not overwhelmed at the last minute. Two questions:
1. What's the longest I can freeze them without risking the cakes getting soggy?

I have fzn cake for that long but don't recomment it. Wait 2-3 more weeks. BTW: they won't get soggy....they will get dry and hard if they are fzn too long

2. Is it ever ok to freeze a cake with buttercream already on it or will that create water droplets?
Yes, cakes can be fzn when iced w/b'cream. Not recommended but can be done. Best thing to do is bake cakes; cool, fill, stack, wrap & fz. About 3 days before wedding, remove from fz, defrost still wrapped, then proceed to complete by icing & decorating. They can sit up to 3 days on counter top if home is AC'd.
Of course, ideal would be to do them the day before, but adding an extra day or two is helpful and o.k.
Make all decorations you can ahead....even most b'cream flowers can be made ahead and airdried.