This section of the forum is specifically for help with what ULib and ULX can do and how to use our specific releases; we can help with targetting, but the rest of your questions might better be asked in developers corner (if you wish to write the code yourself)
I've seen discussion of some of your questions, and you may wish to check out the Releases section of our forum.
You can use this google link to search only our site - our forum is well indexed.
https://www.google.com/?gws_rd=ssl#q=%2Bsite:forums.ulyssesmod.netThat will load a google page with our address in it - add a space and your search terms
Using the above link with terms "pvp godmode" found another discussion -
http://forums.ulyssesmod.net/index.php/topic,8710.0.htmlIt has code in it to help with majority what you want regarding PVP during godmode and noclip.
If you need help with it, go to developers corner, make a new topic, reference that discussion, and ask what you need.
You're on your own for anti skybox code - I've not seen it discussed here, but if your learning to code, Developers corner is the place, if your asking it be done for you, Off-Topic is the place.
ULX doesn't have that capability.
As for targeting other players, if you read our readme.txt for ULX, and if you follow it's suggestion of using "ulx help" and "ulx usermanagementhelp" from console as superadmin, and our forum FAQs, you likely would have seen use of the self character "^" and how can_target works.
Instead of giving guest users access to "ulx god", you need to give them access to "ulx god ^". That will limit them to only performing actions on themselves.