First thing, play only 10 minutes and longer games. After every game, use the Game Review. Playing plenty of games without review don't lead to improvement as mistakes are repeated.
Looking for Improvement tips from strong players

Very wrong. Both are necessary, none is more urgent than the other, and one should not pay a dime about his/her rating until he/she can get a good grasp of the game.
I assume if you've been playing for over a year you have a grasp at the game...
Wrong again. You can find truckloads of players who are playing here for several years, and they are rated around 400, or so.
So I need to use several minutes per move? I thought that was bad, as I might then lose on time, but I'll practice that. As a side note I usually panic if I'm losing or don't like the position, especially in live games. Any advice for that?
Play longer time control. Also, don’t resign when you don’t like the position. For example you are down a pawn in the opening. Don’t resign quickly, because when I was at your level, people were blundering after that.

So what would warrant a resignable position at my level? A queen blunder? Or is there none such thing at 800 or below
So what would warrant a resignable position at my level? A queen blunder? Or is there none such thing at 800 or below
Maybe queen blunder is worth resigning for, but still there is a winning chance after your blunder.

So what would warrant a resignable position at my level? A queen blunder? Or is there none such thing at 800 or below
Actually it's your choice, but sub-800 players really love stalemates.

Very wrong. Both are necessary, none is more urgent than the other, and one should not pay a dime about his/her rating until he/she can get a good grasp of the game.
I assume if you've been playing for over a year you have a grasp at the game...
Wrong again. You can find truckloads of players who are playing here for several years, and they are rated around 400, or so.
Then I'm not sure what you mean, because everyone understands the game, it's mostly a matter of reading the board and basic strategy. Emphasis on mostly, obviously when you get better it's going to get more and more complex, but this is a good place to start.

I'm pretty sure you understand, but just in case what I'm trying to say is you usually only need to know one or two openings and basic opening strategy. From there it's tactics. As long as you know how to play the opening you can usually figure out what to do. At least in my experience.

I've been focusing on two books: Chess Fundamentals, by Capablanca, and Modern Chess Strategy, by Pachman. I don't study a lot at a time, but find that even a couple of pages or lessons at a time are extremely helpful.
These are excellent suggestions. This chap thinks very highly of Capablanca: http://chessskill.blogspot.com/2021/01/advice-for-beginners.html

"If anyone has books" ++ "Bobby Fischer Teaches Chess" - Fischer,
Actually Stuart Margulies & Donn Mosenfelder, with RJF not authoring a single line.
For the record, a very average book, at the very best.
And very limited, dealing only with the simplest checkmate patterns.

Any suggestions for solid openings for black that don't have much theory I need to learn?
try the osullvan gambit simple yet powerful opening

Any suggestions for solid openings for black that don't have much theory I need to learn?
try the osullvan gambit simple yet powerful opening
How can one play a nonexistent gambit?
If you mistyped "O'Sullivan", then this site is about chess, not snooker.
Any suggestions for solid openings for black that don't have much theory I need to learn?
try the osullvan gambit simple yet powerful opening
How can one play a nonexistent gambit?
If you mistyped "O'Sullivan", then this site is about chess, not snooker.
This is my first time to hear of that gambit. Can you tell me the first moves to it?

Any suggestions for solid openings for black that don't have much theory I need to learn?
try the osullvan gambit simple yet powerful opening
How can one play a nonexistent gambit?
If you mistyped "O'Sullivan", then this site is about chess, not snooker.
This is my first time to hear of that gambit. Can you tell me the first moves to it?
google it on youtube man a really cool opening trap
Question: what has a book told you that actually helped you improve?
For me, The Complete Endgame Course and Reassess Your Chess by IM Silman taught me a lot.
-Jordan