Hello: #1 Good!
#2 If you could readily unscrew them to teflon the threads and reinstall them, checking later would be easier.
#3 Just have a look at the nipples on the tank when you have it in hand. You’ll see if it has heat traps.
#4 It likely is a 50 gallon tank and swirling dip tubes won’t do much unless you take tub baths. If you have naturally soft water, sediment may not be a concern. I’d see how much your old tank has in it and use that as a guide. In my area, I’d always set up new tanks with a curved dip tube if there was going to be someone around to use it.
#5 If there is moisture in the concrete, a piece of linoleum or some other thing to keep the steel of the tank dry would be good.
#6 The T&P is industry norm. I’d keep it and test it yearly. When it leaks, then replace it 😉