All Adobe video products are intended to target consumer formats through Adobe Media Encoder since CC 2014, After Effects has almost only intermediate formats now in its internal renderer (which is essentially the exact same thing as the one in AME).
Instead of clicking on "Add to Render Queue" you click on "Add to Media Encoder Queue" and in AME you will ...
This is a fast way to copy the clips in succession.
Copy the video clip CMD/CTRL + C
Target ONLY the track that the loop will be on
Then swiftly insert it multiple times by just holding down CMD/CTRL and pressing V multiple times in a row
Building on the cut/paste workflow. You could create the clip in AfterEffects and make it very long. Then just dynamic link to your project.
This way at least -every time you need to use it- you don't have to copy/paste over again. Just drop the one clip and size to need. Also can be useful if you need a varying opacity through the clip, since you don't ...
That's the project window (not to be confused with the media browser, which you can use to browse your computer and import media assets into your project). You can add or remove assets to your selection by holding down CTRL / CMD while clicking on them.
Short answer: You can't. Unfortunately, there is no way to save a project so that it can be used in older versions of the program. That's a major downside of Premiere Pro, especially since this is possible with most other programs of the Adobe Creative Cloud (InDesign, Illustrator, Photoshop, ...). But at the moment, you can't do that with Premiere Pro.
Buttons will automatically allign to other button ontop or under existing buttons.
Right now they are not aligned because you are missing a spacer after the first two button in the bottom row. Or remove the spacer in the top row by dragging it into the editor window.