CO2 tank question and connections

Ok So I managed to keg for the first time today. Things seemed to go well for the most part. I using the flex keg setup from here. 5lb tank. Do to an injury I was not able to build out my mother of all fermentation kegerator at the time so I am using the serving fittings that came with the keg kit. Forgot to check them to make sure they were tight before connecting so sanitize. Small mess but easily fixed. Now the hose kit came with 4 small white Teflon/nylon seals. I was not 100% on were to place them as nothing was mentioned with the instructions that came with. So logic told me the gase side connection to the regulators should get the fittings for sure but I was not what to do with the other 2 as I was worried about damaging the plastic serving taps since the fittings was plastic wrapped in metal. Was there a specific connection I should have used them remaining two on or were they extra? After all there were 2 tank nylon gaskets.
And last question how far do you guys typically open the tank main valve? Half a turn does not seem like enough… The sanitizing direction had me do that.

Also based on my reading are leaks are to find? I used both soapy water and sanitizing solution, poured and sprayed everything looked tight, but some folks make it seem like they are hard to find. But they should be pretty obvious if your water is soapy enough, but I never checked for leaks at 5-10 psi. I used to slightly higher pressure in aircraft systems.

Looking at the NB Flex Keg system pictures, there are white nylon washers that are attached to the regulator assembly pipe that attaches to your CO2 tank. One of those washers is supposed to be used for the connection to the tank. You say NB gave you four of these? Not sure why so many…ideally, you should replace the one between the tank and the regulator every time you refill the tank. I do that probably every third or fourth time I refill my tank.

As far as the tank main valve (the one on top of the tank), open it all the way.

If you did not see any leaks after using the soap solution, you should be good to go. But, make sure you have the washer between the tank and the regulator assembly installed. Without it, you will definately have a leak.

Good Luck.