When I got my Z a few years ago, it had been sitting for a few decades (under 2k miles in 37 years). I dropped the fuel tank, cleaned it out (luckily it was in great shape). While it didn’t really it, I used POR-15 tank sealer, only cause I had previously bought it.
Then I replaced nearly every hose, rubber, seal, gasket, and suspension part. I think the biggest surprise was that the motor actually ran, prior to me replacing the fuel filter and replacing the carb gas filters. They were completely clogged up with orange rust. The fuel filter was replaced 3 times before it finally stayed clean. If you need braided hose’s I used Bel-Metric in Mass.
For buying/selling I’ve never had an issue with PayPal.