I would use "other" ones structures the same like other ones coaster-designs. More for inspiration than only simply adding them.
Sure, people like "Belotto" create amazing looking buildings, but if the project is somehow up for download than i would prefer to build my own buildings. And use "prebuild" structures only for privat projects.
Well, if you use a building/structure from a other user, than its necessary to give Credit to him.
Doesn't matter if you use the whole creation of him or being inspirated. So if you use for example "Belotto's" creations than Belotto should become credits for it.
A CS-List is allways needed, but only one for the whole project should be ok. Easy way would be to make ascreenshot of your "Style/Themed" folder.
DiarugaCoaster did this in the past for his wingrider "Shadow". It works well.
Or the longer way, wrote down every single set that you use in a readme and/or description.
If i am right, than there is a program, called "ParkCleanUp". This checks your scenario/park which sets you use and create a list and alos it deletes every file that isn't used any more in the park.
Because if you placed some rocks for example, and after a while you delete them, than the rocks are gone, but some datas about the rocks didn't gone and make the park-file lager than it could be.
With "ParkCleanUp" these invisible file thingy will be deleted and your park-file will be much smaller in the end. So a safegame with an size of 20MB, can be shrunken down to 10-12MB with this.
"Park CleanUp 2"
Cheleste