There is a shutoff valve on the cold pipe going into the H/W tank, if you close it no water will come out of the tank. There should also be a shutoff valve on the wall below each faucet/tap.
get a plummer to look at the problem
It is not common to hear a bubbling noise coming from you gas tank. It may be that your gas tank is too hot. You need to stop your vehicle and let a professional look at it.
No this is not necessary. Install the pipes as per usual. You can insulate the hot water pipes up to two meters or up to two yards from the hot water outlet from the hot water tank to prevent this. No this is not necessary. Install the pipes as per usual. You can insulate the hot water pipes up to two meters or up to two yards from the hot water outlet from the hot water tank to prevent this.
Install a tempering valve in water line feeding toilet. Tempering valve will mix hot and cold water together so warm water fills toilet tank which will stop condensation.
Try cleaning out or changing the aerator on the bad one.
The hot water tank might be undersized for your usage.
do they help with hot water tank replacement
The hot water usually goes to a storage tank. The PRV goes there, near or at the top.
how long does it take for hot water after lighting water tank its gas?
Replace it or turn your Hot Water tank temperature down
You can, but you don't have to. If no hot water is being used it will not come on that often and will just keep reheating the water in the tank. Is there any chance of the water in the tank freezing? That would be a reason to leave it on at least at the lowest setting.
No, a hot water tank heats water by itself.