Thats too dark I’m afraid. You could always add a _minlight value, or add an ambience value in your worldspawn that would lighten things up a bit, but in a cave, lights are your friends.
Have you asked yourself what kind of objectives this map would feature? Or what kind of layout?
Its always good before begining with the basic designing of the map, to sketch down a little overview of the map, write down where which objectives are going to be, think whether or not it is wise to place the axis spawn here or there, small things that help you when you start making the map itself.
Do you want to make a single cave where the axis and allies fight it out, or do you want to make a few intertwined cave systems where some of the objectives are, but the allies have to fight their way inside?
All these small things help you during your designing of the map, and if you ever forget what you actually wanted the map to be, you can always return to your little piece of paper with ideas and sketches.
Atleast, thats what I’ve found most useful.