I would rather see you get a digital where you set the temp than a dial where you have to work out where 99.5 is. It would work but wouldn't you rather set 99.5 and then get to see what the temp is.
no you need a digital temperature controller not a thermometer. What you have listed will show the temperature what you need is something to control the temperature.
Do a ebay search for a digital temperature controller
personally I like the ones with 4 digit displays because the 3...
A hot water heater works with in a band so it will turn on maybe 3 degrees lower than what it will shut off . This is to avoid constant cycling the water heater and reducing its life plus no one cares about the tap water being 3 degrees different. Modern digitals can be programmed to switch on...
avoid the water heater thermostat if possible as that's a old school way to do it. Digital temperature controllers are a lot cheaper now so every one uses them. If you have no electrical skills you can buy controllers that are set up with a receptacle so its plug and play.
bulb size is...