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I don't know if making a map pack with custom monsters and weapons and shit is too much for someone so new. It probably is.
It is highly recommended that you start with the basics and get those down to a somewhat decent degree before you start working in custom assets that may or may not be more difficult to use.
Starting small basically always works in your favour. That also means it might be a good idea to keep your project size small, release single maps, rather than pushing for an entire map-pack, to gather some more feedback on what you're good at, and where you can still improve.
At the end of the day, you'll need to decide for yourself how you want to go about this, and what you want in your maps and what you don't want to have, for that matter, but the earlier your maps leave the "vacuum" of your builder of choice, the easier it is for people to help you out when you questions.
Just don't go for the typical 32-level overdetail slaughter megaWAD, that's such a cliche and only sissies do that, really.
Even if it is 2much4u you can still try. Perhaps recruit a few buddies to help you. Even
whenif you fail, you can still draw some conclusions from it and, hey, have some fun in the process.
You should try participate in some not so strict projects. People would play your wads and give you quick advices how to improve your work and you could learn. When I built my first map, I thought I will create something big and mind blowing, but I was wrong. You can always ask for help if you struggle in map.