Welcome back!

1.) Best way to do it is with
r_gamma 1-2 and
r_intensity 1.2-1.4, depends on your setup. Old Quake may not be best for today's systems, so recent ioquake3 is highly recommended, it also provides OpenGL2 renderer, which will produce brighter and better picture without any extra settings - especially noticeable if you run Q3 in a window.
For some reason they still have old version from 2009 (without OpenGL2) on their main page, but you can get the latest version here:
https://ioquake3.org/get-it/test-builds/ ... Any recent version with renderer_opengl2* dll file inside ioq3 dir is good. In case of manual install, simply unpack ioq3 to some dir and then copy ./baseq3 from quake3 to that dir as well, that's all.
Note: ioq3 will save screenshots and demos to Windows user dir by default, like
\Users\{user}\AppData\Roaming\Quake3. It also saves to user dir on Linux and Mac.
Further info, along with new commands and cvars:
https://github.com/ioquake/ioq32.) You can connect with
/connect q3.vogon.co or
/connect nw.vogon.co or bind this to a key, like
bind x "connect q3.vogon.co".