Okay, so, node.js.  You stated in your OP that you wanted to create the server software in c++, that cool and all, but I think you will find node.js to be an easier beast to tame for this type of project.

- https is a default library, with webserver modules a plenty if your too lazy to do your own custom routing (express, flatiron, etc).
- bitcoinjs is easily implemented for generating wallets, tipping, etc.
- mongodb provides an easy data model and storage for all your data needs.
- crypto libraries are provided by default
- easily scale-able with the cluster and child libraries.

Not saying the performance will match that of a c++ binary, but will more than likely surpassed the PHP based model we have here, and would be my go-to if I was making this project.

Good luck.