We suggest you choose a platform that can be evaluated easily for convenience. 

Building for WebGL as your primary submission is our recommendation.  As WebGL can take a very long time to get built, you can probably start working on Win64 builds initially. You can submit a WebGL Build as well later on when the game is ready to be submitted. In case you only want to go for Desktop builds, we recommend that you build for Mac and Linux as well.

If you prefer phones, you can submit an APK as well for androids. 

Should you go dedicatedly to VR? Maybe, No. It should be playable on devices that don't have VR as well. More like VR Mode can be something extra.