I'm not sure you need to buy a Kindle. I haven't looked specifically at the lending library but I have accessed the Kindle store via the free Kindle for PC app. (I've even bought a few books that way-then used Calibre to convert them for my eReader.) I don't know if I'd consider it legit to do that with a 'loaned' book though.
As for the email addresses, I maintain once specifically for 'sign-ups'. If I'm happy with a site using that then I'll open a new account with a permanent email. Of course I own my own domain so I can create/delete email addresses as needed. I don't run my own mail server though, that's part of the hosting contract I have. It's surprising how many people think it's hard to have your own domain. Now setting up your own web site might be hard-but getting a domain so you can control your own email, that's simple and can be surprisingly inexpensive. The cost depends on where you register & who you host with-and often reflects the service you get (i.e. a cheaper host tends to have more problems). I go with a mid-range 'economical' host that costs less than $50US/year. Like I said, it's not expensive-and not at all hard if all you use it for is email.