replace the fill valve
it depends on how good the pluming is.
If it is just the toilet that doesn't have water, then the pipes are probably not frozen. If it is the whole house than maybe yes. If you have water at other faucets, look at the toilet and see where the blockage is. Disconnect the supply line under the tank and see if water is coming through the shut off at the toilet if there is one.
the pipes were old, rotten and corroded and should have been replaced years ago!
It's probably the original bath and the steel pipes are corroded and leaving mineral deposits in that bath. Other pipes may have been replaced.
to your toilet
If pipes are frozen no water can flow, so water meter shouldn't be registering anything. But if pipes are frozen it's a good idea to turn the water off at the inlet. That way you have a chance to discover and leaks and damages when the pipes thaw w/o getting the whole place flooded.
yes they are
yes
You will probably clog your toilet or pipes if you flush anything but toilet paper. I would not recommend trying to flush underwear down the toilet.
yes if you eat them
depends on what type of piping you are talking about. Are you talking about frozen pipes bursting or High temps??
Toilet paper dissolves so as not to clog up pipes.