2: Did you register your Entity? Because when you spawn a Entity on the server and you didnt register it it will not spawn on the client. Minecraft automaitlcy spawns Entities on the client when they are spawned on the server. And if a Entity is on the client it can actually only see what you see, when its on the server it can see what is on teh server and things you actually maybe can not see.
3: Entity Renderring allows you to render with OpenGL how you want to render things. You dont need a finalized model to render everything. Thats just there to make simple shapes easier to do but complex stuff is PureOpenGL renderring. So yes its possible but i am not as advanced with openGL to do those kind of things. I can do simple shapes with PureOpenGL but anything complex like you want is for me impossible.