If you are familiar with the Forge mod workflow, you can get a Sponge server and client running in a few minutes. What I read in the forums, it’s not recommended to start working on plugins yet because of the unstable API.
I stumbled upon a little quirk in the setup of my workspace, you can read about it at Setup of workspace failed: "assets/indexes/1.7.10.json File not found" - #6 by plzHelp