Giving yourself this huge project isn't going to end up well. You
will end up ragequitting.
You don't have any specific custom content to use, probably no modelling and texturing skills either. Even though you would finish this project, it would end up looking bad.
I don't know have you mapped before but you need to give yourself an easier project. Do something small to improve on your skills. Like I said, you will just end up ragequitting.
If you're still wanting to go on, good luck!