You sort of answered your own question. You need mapping skills in Hammer, which makes up 90% of the work unless you're planning to do lots of custom props and textures. You're unlikely to need any programming unless your adding additional functionality to the engine that doesn't already exist within hammer. Voice actors are something you only really need when the mod is close to completion, as you're bound to make changes and sacrifices along the way that ultimately change the script.
Unfortunately, I doubt anybody will just make a mod for you. You're going to have to bring something more to the table than just an idea I think.