Again, slow down a tad on some things and think. One hose seal will likely get you there. If not, 2 will do. Thin nylon washers with the same ID/OD can be had at any hardware store if you want to get precise for far le$$ than what you are considering. Highly unlikely that you'll ever use all the "up" available to you on the platform you now have. YMMV.

Yes, push into a bipod for a number of reasons. Similarly, I don't own one.

Push some quality fodder through it to see what's what. I'm off to tend to other things.