Please don't let me discourage you, but....
I worked as a software engineer at a leading corporation specifically within web services for 20 years before I left to start making a game. From what you've said, I'm guessing that you're new to web services and data storage needs? Do you have anyone working with you (on a dedicated basis) who has mastery over web services? Is this also your first game? If the answers are Yes, No, and Yes... my honest advice is don't include server elements for a hack and slash game. Concentrate on putting together a first class single player experience, and you may find it's a freeing thing for you. We did, anyway. (If you'd like to read about how we reached our decision, we published an article at
http://www.dawnofthefel.com/blogs/indie-games/frenemies-with-benefits.) And this is even though I have 20 years experience in this area!
Basically, the moment you include a server element in your game, you open yourself up to multiple hard-to-predict attack vectors, and all the time you spend working to counter those takes you away from making your game. Also, you incur an ongoing operational expenditure to maintain the servers.
Of course, if the answers to my questions above are different it changes everything!
Either way, best of luck to you!