mrwonko

If you just want to globally increase the brightness you can use the "ambient" setting in worldspawn (increases brightness everywhere) or "_minlight" (prevents dark areas without brightening light ones). Another possibility is having a sun (either via shader or as a directional light entity with the "_sun" setting) and using the -bounce parameter of Q3Map2 to simulate indirect lightning.

Can be disabled with the center button in the top icon bar, the one that's enabled in your screenshot. I believe the distance can be varied using [ and ], which means I can't do it on my German keyboard.

I'm saying the JAPack included with Radiant and installed into base contains JK2 models but not their textures.

You don't need to decompile the map to change the entities, that's what Q3Map2's -onlyents is for.

textures/common/env_glass_security, I think. A quick look at the .bsp in a hexeditor helps.

I hate just giving an example without explaining how or why it works, so instead of giving you shader code I'll explain the concept.
Making a texture shiny is achieved by overlaying a second, transparent texture that then moves around (the reflections). To then prevent certain parts from being shiny, you could overlay another texture with transparent parts on it. The non-transparent parts would thus hide the shininess. The exact shader varies depending on whether you need a lightmap etc. You're thinking of an on-character HUD akin to Dead Space? Having procedural shaders is not unheard of: Jedi Knight Galaxies has weapons with Ammo Counters and Hydroball has the in-map scoreboards, but this requires code modifications which make it pretty tricky if you're not into coding. I would assume this requires coding as well, but I don't know for sure.