First one is$doable since a hong time - trick is to catch < > keys when they are pressed and send request to server to refresh client fov via RunServerScript(). Key pressing must return to client/gui, so the actual direction change will happen.
As for other things, i'd put it on hold fov a while and wait until both things (inventory and leftmouse menu) are moved to scripts, and then modify it to your needs if it won't be possible out-of-box.