There's also a console command: hideactors

That will hide your weapon and any npcs
(npc = non player character)

If you want to fly around, use the console command: fly
To walk again, use the command: walk

Access the console with the ~ button (to the left of the 1 number key).

Where? What's the setting?

You can find it under Preferences > Video > Font Size / Translator Size

Or you can just use dgVoodoo or nGlide. Pick a resolution in the game with the HUD size you want, leave it at that and in either dgVoodoo or nGlide, pick whatever resolution you want and the wrapper will scale everything automatically.

Currently playing in 1920x1440 with the same HUD size as from 800x600.