I have used o-rings under the centre post before to make sure there's no wobble and it cannot touch the threaded part of your atty. Your last pic looks like it's not doing that, just make sure you are not screwing it down too hard.
O-rings in the catch cup are unnecessary, but advised for 2 reasons. One - it keeps the juice confined to a specific path. Two - it allows you to align the airholes on the atty where you like, which is typically away from your face, so that you don't get little hot splashes of juice on you when you fire it. It also means there is less chance of screwing down the atty so hard that you ruin the gasket in the 510, which will also cause a short.
T
