Are labels a loss?

Nope, most people don't pay attention anyway.

Not tacky at all. My FH and I used labels. Most people are going to throw the envelope away almost immediately and won't even care.

We used clear labels for all of our wedding mail (stds, invitations, rsvp cards, thank you notes) - my handwriting is atrocious and it's a LOT less expensive than a calligrapher

That's what we used.

If people had a problem with it, we never heard about it. Honestly, I doubt people even noticed.

I'm buying a stamp for our information and then handwriting our guest information for STDs. But having it printed on the envelopes for invitations.

I don't think so, I think it's totally fine.