Welcome to the forum. I think most people are using 5l/m concentrators.
As far as the valves go, I feel like they aren't bidirectional. But I'm not sure I understand what you want to do with them. Flashback arresters are intended to keep fire away from unburnt gasses, so it seems to me that it only makes sense to have them in the same orientation as the ones at your tanks.
And also, if fire is coming out of the torch, don't let go
