It could be a thousand things - take the ignition module off and take it some place where they will check it for you.
Check the crankshaft sensor.
Check the ignition switch.
Well, we know it is the belt. And if you have an idler pulley, then we know the belts are tight. So replace the idler pulley. It doesn't cost that much and it isn't that hard to replace.
It depends on what kind of paint you used. I wouldn't think that latex paint would bother them, but a solvent based paint would be a different story. Check the can's label. If it says that you should used in only in well-ventilated areas, then get your canaries out.
A bird's respirtory...
Easy enough - An iron frame should be (but not really, because iron is not as strong as titanium, so that an iron frame would have to be thicker, and a steel frame would be stronger than an iron fram, but I have strayed from the problem) made with 512 cubic centimeters of iron. Find the density...