We decided to put a w/d unit upstairs and a separate electrical panel.

I just think you did a cheap renovation and it shows, I mean you painted over wood panel, no granite in the kitchen, old cabinets w no knobs, you didn't open up the space between the living room and the dining room, you didn't tile the bathroom shower, who knows what the vanity looks like and its a 2bd/1 bth with a house in a not great area. 

Recently, we have solar panel installed on the roof, and the room temperature drop at least 5 degrees.

We are changing panels and adding one more, switching to GFCI outlets, etc We will have a temporary hookup after the village inspection and before the power provider's inspection.

I didn't think it was too big a deal but my house has this composite paneling on all the walls that I'm replacing with drywall to make it look nicer which is taking a lot of time and a little bit of money. 

Main things you would be concerned about would be an old panel with screw in fuses or one of the old breaker type panels that are known to fail.

Maybe even look into some vinyl faux stone panels if they are cheaper so they don't stick outward from the wall / stairs.If you go too specific to a taste too it can turn someone off & have them think, 'well thats one thing I have to replace' that is not my style

But they are also ugly, noisy, and expensive to run, so it depends a lot on the class of property and what your goals for the property are in terms of repositioning.It isn't always as simple as just slapping in a central unit; Electrical panel and/or service upgrades are sometimes needed, and you need attic or crawl access for duct work and returns, as well as a place for the air handler to go (which often means giving up a closet). 

Be ready to get a calls about the “solar panels are broke, please fix” every time the grid is down for an hour or two.

However, both electrical panels are located in one unit and utilities are paid under one bill, not separate.