As they say...if you have to ask the price, its probably out of reach...hopefully not a troll question.
The electrical question is fairly unknowable without more details, is the panel inside the garage, or a finished part of the residence, are there extra slots in the panel, what's the distance...could be $150, could be $1000 if you had to open up walls, etc. Difficult to guess
Heater. I'm going to guess it will have to be electrically heated due to no sidewall penetrations, living space over garage, no way to install a gas burner, wrong to install anything ventless due to moisture push. Probably 300-500 for something like a 4-5kW heater, another $200-400 for electrical work.
Paint. You doing the work or someone else? It could be as cheap as a couple gallons and some other stuff, $100. Pay to have it done and I'm going to guess $300-500.
Insulate walls. I'm going to guess stud walls. If you do the work, $200. If you pay to have the work done, $500+
Garage door is probably in the $1200-2000 range, installed.
Wall opener and epoxy, have to google the price. No idea if you are installing or not. Guessing not.
I know there will be posts saying paint, wth? $40! Maybe so, everyone's ability to find materials and contractors willing to work for nothing is different.
I'd set aside $5-6k and hope you come out with some at the end to get some toolboxes, aquariums, etc.