Resolution and Sprite Help

I've been searching for an answer to this for a few days and am having trouble understanding it.
First a little about me.
I don't know to much about the unity engine - and I'm an average coder, learning through well - coding games. As I've messed around with some you tube tutorials, some of the tutorials here on unity it's self and as well some courses through Udemy.

I have an ever lasting goal to create a nice 2D RPG the biggest set back i have is I'm not sure about how to go about doing sprites. I can write as much code as I like to get things flowing correctly, but I don't exactly want to make a ton of art over and over as i'm not the greatest artist at all.

I want my game to primarily be for Desktop Computers. - No Mobile, console or anything in between as of yet.
I want all my art to be created from hand by my self without the use of any free assets, so that is obviously going to take a lot of time, so I want to really do it right the first time.

Questions. --
1. I don't exactly have a "target" resolution, and I know that unity allows the players to pick what ever resolution right before start up. how ever from searching this topic ive read that when making any sort of 2d or pixel art the sprites can get scaled up where they look horrible at higher resolutions such as going from 640 to 1080.
Now as I stated i don't exactly have a target resolution, how ever if i were to pick one it would be 1080p as in my mind it makes more sense to allow a downscale rather than trying to upscale something.
Would this be a logical choice?

2. If i target for 1080p that way when someone loads up the game and clicks any resolution bellow 1080, it downscales? What should my sprites/sprite sheet be made in in terms of pixels?

3. If im using a "top down" and allowing them to traverse both x and y axis how will i go about the sprite/camera ratio in terms of size. ?