What's the deal with propane fittings?
Short answer, no.

From my personal experience with replacing the gas line for my water heater:


Don't buy on Amazon. Go to your local store if possible because if you buy the wrong thing (which you'll inevitably do if you don't know exactly what you're doing), returning it is a pain. Besides that, some plumbing products on Amazon seem to be more expensive for some reason.
All pipe should have NPT threads. Lead free brass is only useful when you're dealing with potable water. Gas applications shouldn't matter
I just used black steel because it's significantly cheaper than brass and since there's no water running through it to rust it, it'll work just fine.
Make sure you use a teflon type tape that is rated for gas lines.