An update!!! Sort of!!!

So eventually I will get to actually starting this edit for real. I’m still using a laptop and I don’t have Adobe CC yet. Hopefully in the not too distant future this will all be remedied!
However, I did start the 7 day trial of After Effects 2019 and Photoshop. I’ve used earlier versions before but I wanted to just play around and test out a few VFX ideas.

I’m hoping a few experienced members here can help me out with some answers. I’m a noob at a lot of this stuff!

With the amount of visual manipulation I plan to do in my edit, I should really be working in 720, yes? I ripped AOTC using MakeMKV and it is of course 1920x1080 at around 30 or 40 GB. I shrunk it down to 1280x720 to around 11 GB.
Does this seem about right? With certain shots I plan on manipulating (and in some cases, zooming in) should I be using the 1080 file? Is there anyone here who is working at 1920x1080 and doing effects heavy work?

As I watch the original file (the one I shrunk down to 720) it looks fine to me. It has the “black bars” when I watch it in full screen mode. However, when I rendered out some unfinished tests, something about the aspect ratio seems off. The film is stretched out to fill the entire screen (no “black bars”). My composition settings are in 1280x720 with a 16:9 ratio…(I didn’t adjust any settings in the composition settings)…so what am I not understanding?

Another question: When I watch Adywan’s ESB, there are no “black bars” when not in full screen mode. How is this achieved? And for what purpose?

I sure would appreciate some help…or at the very least, maybe a link to some place that may have answers?

Thanks!