I applaud your resourcefulness, but will caution you on the perils of doing your own gas work.
Although propane has ingredients added to give it the smell we all recognize, sometimes it does not get noticed in time.
I'm pretty resourceful myself, but won't mess with gas lines at all and will only go as far as replacement of a connection pipe.
I get the waiting for contractors and the crazy prices charged, but messing it up may cost much more.
But, if you're confident in your work, so be it.
I agree with your premise. And that was the reason for my hesitation and my willingness to pay someone who does this for a living, and therefore the expectation they know what they are doing. But I have also experienced contractors who send out workmen of questionable talent and or experience, but no need to get into that. If I have any reservations about the installation it would be the on the basis of even using a flexible gas piping system versus the black iron pipe. It’s not even the piping itself but the fittings that are used to make the necessary connections. If there were any possibility of leaks this would be the spots. But, as with so many things I have to trust the engineering of the product being produced, and then my abilities to use the products and understand how they are to be applied. Whether iron pipe or CSST it’s really not rocket science. There are people out there that you wouldn’t want changing out a light bulb (exaggeration) much less a gas line, but it’s really a matter of educating yourself and applying common sense. After this initial experience, I would have no fear of future needs to do the work myself.
Good for you, did you use flexible gas lines? Hopefully you added additional shut off valves for just in case purposes. Gotta love natural gas.

I bought a 25’ roll of CSST, two connector fittings, a gas outlet box with cutoff and then I had to go back to get the 24” gas line to go from the cutoff to the heater itself. All the flex line I used, about 23’ was run as a continuous line with fittings on one end to connect to my iron pipe and another fitting to connect to the cutoff valve. All my other connections were threaded connections that use pipe thread sealer. All connections tested leak free! NATURAL GAS, I wish, I’m on propane.