In my opinion, based on the current genres that I have knowledge of
should be alternative/indie/rock music popular in the 2000's to present. Ex. Foo Fighters, The White Stripes, Arcade Fire, Radiohead, Silversun Pickups, etc. Lots of choices to choose from here, this station should be no problem.
if this is the only metal station this would be super easy. Just put on whatever.
classic rock all the way up to grunge. Ex. Led Zeppelin, Journey, Guns N Roses, Soundgarden, Nirvana
if punk is a single station you would have to play older punk and newer pop-punk together. Ex. The Clash, Bad Religion, Green Day, Blink-182
I assume you mean bands like the Beatles and Rolling Stones, throw in some Beach Boys and Monkees etc. Don't know much about artists of the 50's.
PLEASE critique my proposed setup, this is just my opinion and I would like this to actually go somewhere, so if we have multiple people agreeing or disagreeing on something we can establish what will work for the final product and what needs to be changed before launch.
EDIT: Alternatively, if you are considering making Darkness a separate metal station, you could separate the two metal stations something like this:
Progressive Metal, Power Metal, Post Metal, Symphonic Metal, Thrash Metal/NWOBHM
Death Metal, Black Metal, Metalcore, Nu-Metal, Modern Metal