Of course you aren't going to have access to outstanding bandwidth, but I've used it for business purposes for years. Whether or not you would want to use it for business depends on a number of factors, but I don't think you can flat-out say it isn't realistic for any business.

I've personally never had issues with my ISP blocking it, but I read accounts from time to time (in this thread for instance) where people had issues with ToS enforcement. You'll have to evaluate your own situation, or just give it a shot until they explicitly react.

But you are right about email- it's a pain. Most likely you will have a bad time trying to get something authentic-looking working with a home ISP. Even doing it on a legit VPS is fairly complex.