Kilo has given very good advice.
I would also suggest looking at You Tube videos, there are a LOT of them that discuss what each of the settings do, and some of them deal with the resolution, plus a host of other topics.
Wow, there are some detailed questions there, and some outside my knowledge - e.g. SIDS and STARS. I don't use them but know they can be replicated.
You can use keys or speech recognition to communicate, you can change frequencies manually or automatically, you can acknowledge ATC instructions manually or automatically.
Please do try the trial version to find out what it is really like - my words don't do it justice. It is available at Try before you buy - OnCourse Software (ocs-support.co.uk) . I have read that some users have had difficulty installing the demo (perhaps because it works across so many operating systems and Flight Simulators) but check their forum or ask on there if you do.
Thank you, Davidc2! I will check that when I open the sim again. My discouragement led me to shut it down and run errands haha. Your suggestion definitely sounds logical, though I can't imagine how I might have done that (the only tinkering with settings I've done is after the symptoms started). I'll report findings shortly!
i7 2700K, 8GB RAM, Nvidia GTX 1050ti, 500gb ssd.
Before doing anything else, I'll try your suggestion and keep the 2560 x 1440 and turn down the render scale.
That's my problem setting things in MSFS, I have idea what most of those setting are or what they do.