1- Do Shark Bite connections make it a world easier vs sweating pipe joints? YES but make sure you deburr the pipe or you will cut the o-ring. You can also use the double compression if you are using Copper pipe or IP to Gator/Shark connector .
2- How do I insure there is no air in my pipes after installing? Open the HW faucets
3- What is the best way to set up on the stand? Not needed if electric. New gas models don't need them anymore. I just set them on PT 2X4's. If the current one is elevated, keep it the same to reduce piping additions.
You can buy an install kit. You will think the braided hoses are too long after cutting pipe below shutoff valve. Just loop them. You need an expansion tank if you don't already have one
Replace it if you do
From a retired home inspector and things change all the time but used to be each county/states have different codes. Give your code enforcement a shout. They are more than willing to help. I've used shark bite a couple of time and no issues. As mentioned before, clean, deburr, and follow directions, good to go.
I like using the pan in lieu of stands but whatever code requires. Expansion tanks are required in most counties on new installs.
Oh by the way, T&P valves must run outside in downward position with open end of pipe no more than 6" from ground. There again, local codes dictate that rule.
If you decide to sweat the fittings do not use a propane torch. Spend a couple of more dollars and get a Mapp Gas Torch. Will save lots of time and hassle.
Do NOT call your local code enforcement and ask any questions
unless its from a payphone or prepaid cell
most are just revenue collection and will not pass up a chance to pop you with a fine, and calling and giving them your name and address on their caller ID will get you on their radar.
when you call, the first thing they will demand to know, is your name and address, and usually refuse to answer any question if you dont tell them.
I know several cities that pay the trash truck drivers $100 every time they turn in someone doing work on a home with no permit,
like if you have the box the water heater came in , in your trash.
use the shark bite Flex connections, they are very easy, and Ive never had any problem with them. even 10-15 years later.