If you want to run a server in a private subnet, you’ll need to use a VPN to connect to it. AWS VPN is a managed OpenVPN service that can handle this for you, and allow you to lock down public access to your protected instances.
Most cloud providers divide their offerings by number of CPU cores and amount of RAM. Do you need a large multicore server, or a whole fleet of them? Here’s how to go about measuring your server’s real-world performance.