Avoiding legal risk, it comes down to the terms of service and having people who sign up for an account agree to indemnify the site owner/host.
OVH/Google Cloud/Digital Ocean. THey are all at different price points. It comes down to budget and if your content is legal on their platform
Feel free to PM if you have more questions.
You would want to get a good platform like XenForo (which this site runs on) and then create your own functions ontop of that. Farm out what you can and focus on what sets you apart from the rest.