How to legally run a web service that implies making a profit (for example, a monthly subscription)?

Question

Business Informatics

Hello!
Recently I asked myself the following question: "How to legally keep a web service that implies making a profit (for example, a monthly subscription)?". So far, I realized that in any case it is necessary to register an individual entrepreneur or LLC. Should I open a checking account? Do I need to get any kind of license? Is it better to keep servers in Russia (I am in the Russian Federation, I plan to open a service right there, I mean the law on the storage of personal data)? Do I need to notify any government agency that I store personal data? And about the fact that it is possible to carry out any monetary transaction on my site?
And since it comes to that, how long can you do it illegally, at what volumes and what threatens for it?
UPD: How to work with yuriks if you are a web service? Standard contract with everyone? Issue invoices by mail + EDS?