How should I deploy a multiplayer arcade game?

I have a half written arcade game that I was using as a project to teach programming to my siblings. Simple graphics and simple physics and it's quite fun. Needs centralized server.

I want to try to market it to see how it goes but I don't know what deployment medium to use. Should I go with a simple website, a smartphone/tablet app or both?

Thoughts on my options:

Website alone: >accessible only for desktop users >complicated revenue model (don't know how I'd implement one actually since I'm worried that users might be too involved in the game to notice the ads) >needs web server scaling if popular

App alone: >accessible only to the users of the chosen mobile platform >a bit more difficult to implement in my case >slightly higher upstart cost >less personal freedom >easy revenue model

Both: >accessible to everybody >highest upstart cost >hardest to implement >might not be the most optimal revenue model >>i.e. otherwise app costumers accessing it for free on their desktop systems

And finally, what steps do I have to partake legally not to get screwed over in the remote eventually that my game becomes popular?