Hello, I have made blocks with custom models before so I do know how to do it, however when I tried to make one earlier when I tried to start the client Minecraft crashed and said that FML encountered a fatal error while launching. Now since I have access to the EE3 source code (as it's open source now (thanks Pahimar)) I did go through and check whether what I was doing was correct, and from what I can see everything should be working. From my testing, this seems to only happen when the tile entity has it's renderer bound to it. Thanks to whoever is looking, code is below. If you need anything else just ask!
Proxy Classes - Tile Entity and TESR Registration
Client:
Common:
Crash log: