I'm going to jump on the "don't coat it" bandwagon. Steel doesn't rust with petroleum products in it, just the water that makes it in. Recommend getting it boiled out and any holes fixed at the radiator shop, then keep it topped off and use a good fuel stabilizer like Lucas.
Recommend you head over to https://www.calculator.net/voltage-drop-calculator.html and plug in all your variables. National Electric Code says anything over 5% voltage drop is not acceptable.
Spoiler, plugging in your run lengths for a 15 amp circuit results in needing some hefty cable.
I used to buy WD-40 that way, in a gallon metal can. The goal was not soaking items in a bath, but was to pour it into a spray bottle, and save money over time rather than having individual aerosol cans.
Big Evapo-Rust fan. My rule of thumb is once something comes out of Evapo-Rust, it gets cleaned in water, and when dry immediately primed. Since the whole reason something rusts is because it loses it coating, I always plan on what the coating will be. If not for paint, I put Fluid Film on it...
That's a tough one. Autobody paint is catalyzed. Something like spraypaint is solvent based and would come off easily with solvent or clay. Like Rust in the Eye said, hopefully there was a layer of dust before the paint.
I've done about the same as you OP, down to it has an inside and outside door. Stiebel Eltron water point of use water heater, 1800 watt wall heater etc. Only thing I would recommend is you say deep sink. I would trade it out for a single laundry/utility or seperate hand washing and utility...
We've already got some subject matter experts that have answered, and I defer to their advice. Having lived this, recommend starting with two people on the outside. One person puts light pressure on the glass and makes sure you aren't pulling the gasket out more as you concentrate on getting the...
Rent an electrical concrete circular saw at Home Depot for $89 a day. Cut a 12"x12" hole inside your building where your panel is going. If the saw doesn't go to the bottom, finish with a sledgehammer. Now the conduit can 90 degree into the building into the panel with no LBs, and not visible...
There are plenty of fart fans installed in garages to get rid of humidity or fumes. Fart fans also go into conditioned bathrooms. Install one of those, and they have built in dampers.
They make 4" rubber strips that are thin. These would be adhesive and screwed between each panel you want to block the water from coming through. When the door is up, these will be mostly flat, when you close the door they will bunch in the middle. Note that water will stay in this rubber diaper...
If the Liftmaster 8900Ws can use the standard Liftmaster 888 wall controllers, it gives you the learn button right at eye level instead of having to get a ladder to add/remove a remote