Recommended platform for submission

For the convenience you should always focus on a platform that can be evaluated easily. We recommend Building for WebGL as your primary submission. But WebGL Builds can take a very long time to get built. So you should probably start working on Win64 Builds initially.  Later on when the game is more or less finished you should have a WebGL Build as well. In case you like Phones You can provide an APK as well for androids. In case you only want to go for Desktop Builds we recommend that you build for Mac and Linux as well.

Should You Go for VR?

Short answer No. 

Long answer, Maybe? But it should be playable on Devices that don't have VR as well. More like VR Mode can be something extra. But discouraged.