4) You will need to have on hand toilet repair tape, small gas torch, solder, flux, plumbing sandpaper, pipe cutter, gas tape (to seal gas line) and maybe some pipe glue. Ask the sales person at the hardware store for a more defined list.
There are two, one on each side of the toilet, closet bolts which hold the toilet to the floor. If there are caps over the bolts, remove or pop them open. Using a small crescent wrench unscrew the nuts from the bolts. Alternate side to side when unscrewing this will be much more important when reinstalling the water line repair bolts but alternate anyhow.
Unfortunately, people will band together to gain support on something regardless of whether or not it is true. In this case, one person shared their thoughts on how ineffective the letters are and yet, they had nothing but their opinion to support this. They found a group of willing listeners who quickly became active supporters of the belief.
Working on the gas lines is also a complex job that only a licensed plumber can handle because it is very dangerous. Small leaks can't always be detected by odor alone, but a licensed professional has the proper equipment that's needed to ensure that you don't have any leaks in the line.
The first step in the replacement project is to turn off the water line repair to the toilet and flush any water that may be in the tank. If you forget this step, you will have a giant mess to clean up! You should now disconnect that water line.
If you plan to replace fixtures, you may be able to do this on your own. Buy the same style or functional fit and then turn off the water to make the switch. Follow the directions provided by the manufacturer to get the job done.
The plumber you hire does not normally do heating but will do hot water heating or in floor heating in the house. Some places you can use the water heater for both domestic hot water and for in floor heating if the heating is a secondary heat. Check with your local plumbing codes on this to be clear.