The specs you’ve listed should be more than capable of running a 32 player server. Storage wise though, it depends largely on how many resources you want. The server artefacts on it’s own is less than 50 MB and most resources are about the same (if not considerably less) so I imagine a few GB will be fine.
You can check out the resources available to you in the releases category. The resources you use are very much dependant on what kind of server you want to setup. Most people tend to go for a traditional roleplay server which generally use either RedEM Roleplay or VORP Core as their base framework but there are other options out there and you can always opt to create your own. You’d need to ask in each respective topic for resource specific translation instructions. I know that with VOIPCore it’s nicely set out in a configuration file for you, but not so sure about others.
32 players is currently the maximum you can go in one session. You don’t need to download RDR2 onto your server.
Check out this tutorial from D0p3t on how to setup a RedM server for more information: How to setup a RedM Server.