Indeed, XGUI is now integrated into ULX. No need to do additional downloads or checkouts.
By default, your server (and ULX) will include maps that are included with other mounted gamemode packages, these may not be part of the servers map folder, but included with Steam packages.
Though you can edit out maps shown to the 'votemap' command, I'm not so sure we include a way to show maps only for one gamemode for those with "ulx map" access like your example.
We're Ulysses, we try to admin everything, not just one gamemode.
As for various ULX settings, XGUI controls all the settings we offer in text files.
That being said, if you like text like I do, first check out your server/data/ulx folder for config.txt, and several other *.txt files.
Additionally, if not in your server/data/ulx folder you may
copy some other special *.txt setting files from /gmod/addons/ulx/data/ulx/ to your gmod/data/ulx folder, then edit there.
Last but not least, please, before asking any further questions, make sure they've not been answered in our FAQ section.
Frequently Asked Questions(I know at least one so far has been answered there, which Decicus was nice enough to type out instead of referencing our FAQ)