1. No you don't. You need to forget that you ever used Publisher.
2. Nothing. MS Publisher stuff doesn't open in ANYTHING else. Even on PCs.
3. Re-design.
4. I'd suggest Pages as an excellent and far superior alternative.
5 and 6. Pages is part of iWork, you can buy the entire suite for $49, or just buy Pages from the Mac App Store for $20. I'd suggest getting the free trial from Apple first, in order to give yourself time to learn it.
Sorry to be blunt, but MS Publisher (or MESS publisher as it was known) was the laughing stock of the print industry and always has been, even on the PC side of things. I think it's criminal that Microsoft never made it exportable to anything else (except sorta-kinda PDF), but that's where you are.
You could set up Windows on your Mac, obtain a copy of Publisher and re-open the files, probably (of course the fonts would reset and the clip art would disappear, but that's typical MS Publisher behaviour when opened on a new PC) -- but all you'll be able to do is look at it, pretty much. As mentioned, Publisher doesn't play well with ANYTHING else, even MS's own other products. Sorry.