how formal should the addresses be?

sari9912

We are using informal wedding invitations on a mason jar with the inner tied with twine and no inner envelop. How formal should the names and addresses on the outer envelope be? 

tiny speck

I'd still use titles (Mr and Mrs Smith instead of John and Jane Smith etc.) if that's what you're asking.

Jen4948

You can use numerals for numbers.  Spell out abbreviations though, as in "Street" and "New York" instead of "St." and "NY."