Why cut the pipe? You can just unscrew it and get a correct length of pipe to replace it. If your dad has experience with gas piping he should know about cutting and threading black pipe on the job.

The fuel filter (fuel pickup) is normally attached to a pre-formed fuel line that positions the filter in the bottom of the fuel tank on the "bar side" of the tank. If its on the starter side, that's wrong. About the chain getting loose. Oregon Cutting Systems recommends on their website that all new chains be soaked in oil prior to installation. That lessens the wear of the rivets and other parts of the chain. They also recommend extra lubrication (squirt can) the first use of the day to provide lubrication until the chainsaws oil pump can provide the necessary oil. To adjust the carburetor, start and warm up the saw. Shut down. Turn both mixture adjustment screws in till "lightly seated". Back out both screws 1 1/4 turns. Start the saw and adjust the Low mixture until the saw idles well and will accelerate without stumbling. Adjust the idle speed as needed to keep the chain from turning at idle speed. Then adjust High speed mixture to achieve full power, keeping it on the rich side.

Yes diameters need to be known. If you really want the showers to be balanced, you should use a manifold for both hot and cold lines and have a separate hot and cold line to each room.

On the surface, that sounds a little crazy. The actual work involved with relocating the gas service is pretty minimal and shouldn't take much time. In most jurisdictions, it's the type of work that technically requires an "over-the-counter" permit, but more often than not the contractor would suggest not pulling any permits, as it is such minimal work. But that might not be a feasible strategy for a multi-unit dwelling (see below). The complication with gas service is that unless you have your own gas meter, there probably isn't a cut-off valve that turns gas off for just your unit. So, even for this tiny bit of work, they'll have to turn off gas for the entire building. And after completing work, they need to do a pressure test to make sure they didn't introduce any leaks. Again, this takes extra time, while everybody else doesn't have gas service. Turning gas back on is another wrinkle. For modern appliances that have spark igniters or glow bars, it's a non-issue. But you don't know that that's what everybody has. So, somebody needs to walk through the entire building and make sure that pilot lights are lit where needed. I don't see how this would cost $5k. But I can see how it is highly disruptive and how it can take a lot longer than you'd think. It quite conceivably involves pulling in the HOA to coordinate work. On the other hand, if you can turn off gas for just your unit, then most of the above becomes a non-issue and a good plumber can have you up and running within less than a day. And it only should cost a few hundred dollars. Out of interest, how many units are we talking about? Two or three additional units? Or 20, 50? The answer to this question can determine how realistic your project is.