Gen 8 LS receiver

Im looking at doing external upgrades for my gen 8.

If I was to get the LS receiver that has a threaded front end does that mean J9 fishbone and outer barrels will go straight on?

Another question is if I had a 10" fishbone what length would I want the putter and inner barrel to be so that I could still fit a hop up and flash hider/suppressor?

Thank you.