I'd recommend one of the sound mods, definitely. Or I"d at least replace a few of the default gun sounds with some other wav files. (Since several of the guns use the same sound file by default.) I won't recommend a specific sound mod -- there are several, and each has some good, some bad -- so your best bet is to just download a few and try them out. Put the particular ones you like in your Data/Z folder (which you'll have to create) and the game will pull the sounds from there instead of the default directory.
You might want gridded terrain too? It can help make reading all the little changes in terrain elevation much easier.
Have fun. I kinda wish I could play these games again for the first time. So exciting.