Step 0.
I use to think I had to build everything from scratch, that is no longer to case today. I would recommend modding a fully functional game with mod support or building with templates and assets from the Marketplace.
Step 1.
If you absolutely want to go the start-from-scratch route, You can get a prototype up and running within UnrealEd with Blueprints, Starter Content Packs, and Free Epic Content & Community Content. I exclusively work in Blueprints. If you do NOT know how to build a simple level in UnrealEd, that is the very first step you should take… Launch UnrealEd and start exploring Epic’s Tutorial to get familiar with it.
Step 2.
Multiplayer would be the next area I recommend investigating. There is Local and Networked Multiplayer. I design my games to use both. Local Multiplayer development is closer to single player development and you can find a good starter tutorial here. Networked Multiplayer should be planned for upfront at the beginning of any project as it affects how you design actor, functions, variables. I found this Tutorial be a great primer on basics, with more advance networking tuts here and here.
Step 3.
UMGUI - Unreal Motion Graphics User Interfaces. You’re going to need GUIs eventually. With UMGUI you can practically create Applications in UE4. VR will need applications.
Step 4.
Once you can build a simple level and put two or more players into it locally/remotely. The first UMG Application should be a Chat App. The Advance Network Tutorial includes a dev’ing a Chat Interface. This will become your first VR Chatroom. Once Chat is working, than you expand on it with a Loading webpages on UMG Panels. Then further expand on it with Game Mechanics Interactivity and more.