Note that most ISPs don't allow it on residential plans, but also won't stop you unless you actually create some kind of problem (no ISP actively polices it). If you're rich you can pay more for a business plan (at your home) which would explicitly allow it.

It's fine to host something for friends on a residential ISP. They don't care. If you want to make it a public website it's more uncertain. Still don't worry though, because they won't just ban you from the internet. Worst you'd get is a phone call telling you to stop it.