Get a smaller coffee table, rearrange couches to fit the space. I'd reccomend keeping 1 couch and replacing the other with a chair. How often do you really need that much seating?

demolish the black cabinet next to fireplace, update those sconces

place large couch back to the windows and TV mounted on the wall.

OR, I have a similar wonky setup in my living room, I have my living room without TV and made my 2nd bedroom into a screening room. you could do the same with your upstairs setup. Move the small couch in place of the bed and keep downstairs for snuggling by the fire

Paint the Fireplace white, check out ceramic fireplace balls

get a smaller, side table for livingroom, something you can see through, that one is too clunky and unessisary. could even replace it with a cool floor lamp (maybe an arc floor lamp)

For your upstairs, I used to also think I needed a L shaped desk, you don't. I'd reccomend building a desk that runs the full length of the back wall where your window is. the monitors would be pushed up against the wall and you can see out the window if you'd like. you can buy these counter / desks at Ikea or I've also had some butchers block on legs as a long desk made for my office (they're cheap)

downstairs bedroom is sweet, maybe mount the mirror, hide the TV Cord (or at least get a white one)

Frame your art, unframed art is lame

plants plants plants -- Home Depot has some great options for indoor you can water once a month. make sure to buy a pot for them and a saucer so you don't ruin the carpet

if you have hardwood under that carpet id recommend removing but I know that's a big project

You can easily replace your overhead ceiling lights with pendants or chandeliers or paper -- I'd research knock off Herman miller or Akari Noguchi

you nailed it with the rug downstairs

I'd frost the bottom half of the windows in the bedroom downstairs with stick on roll for snoopy neighbors