I have looked for 3rd party mouthpieces but nothing exists yet unfortunately.
Yeah, you can choose how it lines up basically.
The metal tube has an O-ring that makes contact with the wooden mouthpiece so you can have it all metal with no wood touching anything aside from your lips.
on the longer stem I go the other way and prefer to have the metal and wood barely connecting but that's mainly because the metal tube is shorter. I'm fairly sure the wood is obviously treated with something as well.
I'll give that a go mate! I'm currently using 4mm balls but I'm always open to getting my hands on some bigger balls.