what if your email changes and you also get a new computer
You should have a permanent email you don't plan on changing then. I have one, I get my bank statements delivered to it, I've sent out resumes through it, I used it to electronically file my taxes, etc. You're going to need one sooner or later. You can change your email in steam if you want, but I guess if you forgot your email password, forgot your steam password, and got a new computer you'd just be out of luck. Gmail accounts can be registered to phone numbers, maybe you'll be able to do a similar thing with your steam account in the future.