Hello,
I am a professional game developer. I have been developing games using Unity engine for 3 years!
Please have look on my portfolio and reviews I have got from my clients :)
Well, this is an online multiplayer game. I always prefer and suggest to use these services for online games:
Photon Unity Networking: online gameplay services, includes chat service too! (server; its not a server though, it a cloud service. Best for Unity and online games)
Playfab: Backend service. To manage player logs, data, progress on server. Its FREE.. It has some nice features like in game news, promotions, player groups, currency, etc.
As you have mentioned, this is not a final product, I can not give you exact workplan, time frame and quote in this proposal.. Please contact me with more details.
Thank you :)