Okay I will be as specific as I can. You need the Wedding Collection File for the Arch, this (when you unzip) goes into the collection file. The other the Community Lot Wedding File (unzipped), goes into your downloads. You will find the wedding arch in build mode in the collection files.
No, you need the Wedding Arch if You want it, and one of the Community Weddings files. When you unzip, the collections file goes onto the collections folder, the rest go into your downloads folder.
When you tell your Sims to "Go to Class" they go to class, but your view stays in the dorm. It's like when in Pleasnatville, when your Sim goes to work your view stays at the house.