what the hell does the car sitting have to do with seafoam? if he put anything in there, it would be a fuel stabilizer.
3-6 weeks is not long enough for gas to go bad (lose its volatility), especially in a completely sealed system. personally, i wouldn't park the car with a full tank, i'd park it with maybe a quarter and then drive down the block to fill it up with fresh stuff when you start driving it again.
for the tires, fill them to 50psi or so and then set them back to normal before driving. that should be enough to avoid flatspotting. again, around a month is not THAT long. even at 35 (or 30, 32, whatever the doorjamb says), they probably won't get permanent flat spots in that amount of time. should be find after a little driving, just like the brakes.
constantly letting the rotors oxidize and then grinding that off is probably going to shorten the life of the pads and rotors, but there's not much you can do about it other than store the car in a dry, climate controlled garage.
edit- also, i saw you said kio rio. those cars are real bad about the rear drums rusting up. when i worked for hertz, i would get them sent to me with 'bad brakes' because they were grabby and the rear would squat down. of course, if you looked at the history you'd see it'd been sitting for awhile with no rents on it. i'd take it out, floor the gas to 30 or so, and nail the shit out of the brakes. problem fixed.