I'm working on a similar type game. C2 can make a very nice client, but the guys are right, you need a server-side engine and a good database design and implementation. I'm not really serious about releasing the game, it's a learning experience for me... and I like reverse engineering some of the techniques others have used in deployed games. My background is the old text muds from long ago, so I have some predigree in the area. Some things I have learnt.
1) the client is fun and pretty, but not that difficult
2) C2 is a good platform for the client, esp if you are focussed on desktop clients.. but you need to look into your connectivity choice.. websockets, webrtc, etc.. some are easier but then they limit the browsers you can use, and how easy each can be used. At least for MMORTS, the latency issues are not that critical compared to peer-to-peer games.
3) you need to clearly define the structure and content of what the game updates will be (eg city -stats, armies, research) and how do you check for valid options
4) the database design is not trivial.. looking at evony (for example), their worldmap is 400x400 which is 160,000 map locations, and say theoretically 10% of that will end up being cities.. big database.. if you need to keep upload/downloading chunks of it to your client.
5) not only is it big, it needs to be fast. hundred simultaneous users could hit your database for actions leading to say 100 requests/minute, but more likely a factor of 5. doesn't seem much but they could be complex searches. Correct database indexing is important. As it is not peer-to-peer, your server will require some horsepower (OR GOOD CODING) to deliver it consistently
6) you need a server engine to authenticate and validate all requests, then you need to trigger all actions in a time-sync'ed manner. attacks need to hit when they were promised, or at least in the order they should have arrived. If you can't guarantee that, or that it will operate in a timely fashion, the game will fail.
so yup.. lots and lots of issues. it's not where I would start if you were new to it... however if you were a good database/server designer, then C2 could be a very easy way to make the client front end.
PS: before anyone jumps in.. I only disagree with VUUV in that I think he's underestimating effort. Most big games like this take 4-5 team members a year to develop - assuming they already have the game engine in place. There's a reason there is no good hobbyist MMORTS platform out there.. or even indie.