What Sneezy said ^
If you don't have much experience with modding or making levels, it might be a good idea to scale down and start off small (mess around and get used to the tools, experiment, and maybe try putting together a level or two). This helps to combat burnout and makes your work more manageable. What you've outlined here is a tremendous amount of work (to the point of absurdity); a single 32 level megawad is itself a massive project.
Having said that, I wish you the best on your doom modding endeavors!