In case you haven't reached that point yet : also evaluate how much network badnwidth is going to cost you if you ever host your servers on aws or gcloud and encounter average success. You may be in for a (bad) surprise.
Now compare that to how much you'll gain from ads. And soon you'll realize one huge issue you're going to have is to maintain your own servers a little bit everywhere in the world.
I've carefully measured and worked toward 1TB/month/VPS at full load. Didn't get there, but now I'm at 2TB (still estimates). With socket.io and JSON, that'd easily blow up to few hundreds TB/month. DigitalOcean for now (but that might change in the future) still doesn't charge on overages, but you do get a slap on the wrist of some kind if you go way overboard, so it's preferable solution to other VPS providers.
It's good that you mention this, since I've heard "horror" stories of people working in this space earning about $10k/mo but spending as much and more on AWS.
Yeah, I've choked one office network on a client project (they went through VPN though) with bot tests. :D
But single-digit TB monthly outbound per VPS was not that surprising to me. Almost triple-digit one in naive implementation, scared the hell out of me first time around. Spent hours double and triple-checking and measuring. :D
Now compare that to how much you'll gain from ads. And soon you'll realize one huge issue you're going to have is to maintain your own servers a little bit everywhere in the world.