While working in the Nuclear Power Generation field for 41 years (machinist for 27 of those years), when teflon tape first came out, it was the “cure all” for any pipe thread job. After several pneumatic valve operator failures, they banned the use of teflon tape and substituted it with teflon paste. The issue was not that the teflon was incompatible with the medium being used, but due to improper installation. The tape must be installed so when tightening the joint, it would tend to tighten on the pipe threads and not unravel. In addition, you must start the tape on the second or third thread so it doesn’t wrap over the end.
All that being stated, I use teflon paste as it is much easier to apply and does IMHO, a superior job.
As for the amount of thread, I shoot for two to three threads tightened by hand, then tighten snug, not gorilla tight. Use a pipe tap to clean and deepen the thread if you don’t get at least two threads. You can always tighten a bit more if you encounter a leak ,but if you over tighten brass, you will more than likely snap it off in the fitting, then you got a bigger problem.
