[Ann Bens]

Run the file through GSpot and see which codec your missing.
My guess its Mjepg.
https://www.headbands.com/gspot/
https://www.mainconcept.com/site/prosumer-products-4/motion-jpeg-codec-785/information-797.html

Edit: sorry this info is for pc, your on a Mac i just discovered.

[Ann Bens]

Select the mono track (or multiple mono clips) in the project window.
Go to Clip/Audio Options/Source Channel Mappings.
Select Mono as Stereo and then hit OK.
Now your mono track has become stereo.

[Ann Bens]

4 cameras is max.
You might want to have a look at this:
https://library.creativecow.net/articles/barrie_jon/Adv_MC_Workflow.php

[Ann Bens]

Premiere is somewhat limited.
Have a look at Red Giant’s Magic Bullet Looks.

[Ann Bens]

Have you tried audio gain?

[Ann Bens]

Use HDVSplit instead of Premiere. HDVsplit offers scene detections and that will get rid of the sync problem.
HDVSplit is an excellent tool.
https://strony.aster.pl/paviko/hdvsplit.htm

[Ann Bens]

Yes, move the clip to a higher track and hit replace bij AE comp.
Change duration of the comp in AE by adding the amount of frames for the handels. Now move the clip into the middle of the timeline and extend it on the left and right side. Add effect and go back into Premiere or render it out.

[Ann Bens]

If you’ve got the Suite, you can use it via DL.

[Ann Bens]

Yes, make sure the stills have the same dimension as the project.

[Ann Bens]

First of all never put your project on the c-drive. One major windows crash and all is gone unless you have a back up. Besides it not very good video practice to have everything on the same drive. Premiere on the C drive and the rest on another drive. See manual.
When you open you project and the files have been moved Premiere asks you to relink them.
If you have not linked them the first time, go to the project window select all the file in one folder and right mouse clik/link media. Locate files and hit ok.