I'd like to point out that creating decent levels and content comes down to experience and plain hard work - a lot of it. If you've never done it before, it's easy to underestimate the amount of work.
So, I'd say, start creating a few basic map layouts and get them up and running quickly. Get a feeling for how much work it is, try to determine what level of quality you'd like and how much resources you can spend on it.
After all, I'd be sad to see a lot of work go to waste because you took on too much from the start. Lack of motivation and proper leadership has killed many mod teams. If you want, you can do some research into that. There should still be various articles available on the subject of mod team management.