You could be a web host as a hobby. Whether you’d acquire and retain any customers is questionable..!
That’s because it’s a competitive industry. There are over 20000 web hosts of various types in the UK alone.
In part, that’s due to it being relatively easy and low cost to do – compared with other businesses. That’s owing to how easy companies like ourselves make it to resell hosting!
Although it’s not our place to give legal advice, please remember that when you start taking money you’ll have to register as a sole trader and start tax self-assessment (at least in the UK). Even if it’s a hobby and you have another job.