Starting a small-scope client/server game with Unity

Hello, I am new to Unity, but I have experience with game development. I am curious about some things specific to the Unity platform, and how I might overcome some challenges - I'm primarily looking for links to resources, tutorials, and other things. I found numerous resources via the wiki and forums, but some things I really have questions about aren't covered.

To give the short-and-sweet overview, I'm looking to do a project involving one or more central servers with some number of clients connecting up to them. The server will take care of game logic and traffic control, the clients will take care of glitz, UI, etc. (so basically every client/server game ever)

I'm not really worried about the gameplay itself (game logic is easy), but I'm more worried about how to do a few things:

• How is a user interface handled in Unity? So far I've seen a lot about laying out a scene, but almost nothing about laying out a user interface, HUD, menu screens, options, and everything else - the glue that holds the world together

• How is client/server networking handled in Unity? The server will be actively communicating with lots of clients, directing their user interfaces as well as the scenes around those clients and everything else going on. Are there some good tutorials specifically for the client/server model? (I have no plans to do peer-to-peer or single-player)

• How is user input handled? This doesn't really seem like it would be that challenging after I look at more reference material, however are there any nice and concise tutorials on how user input works?

• Related to the networking, are there any good tutorials on client/server "load balancing" - or ensuring that 50+ players wouldn't cripple your server with horribly non-performant networking/game code? I know I can find several articles outside of Unity on how to properly do client/server networking (predictive motion, packet combining, etc.) but are there major Unity-specific techniques that I should be aware of?

I really appreciate any and all answers - even if you can only answer one question.