I don't think you have to worry about getting air in the line. I also thought the fuel would continue to run out when I unscrewed the bowl. I had a pair of locking needle nose pliers and pinched the fuel line from the tank, but I only think so much runs out and what I did was not necessary. I think it has a little valve that fills as the bowl is screwed back on. I noticed that when I screwed the bowl back on as the bowl started filling up.
My new filter did not come with o-rings, so I had to used the originals from the other filter. The little o-ring in the middle of the filter, you should be able to remove it by tapping the filter on a hard surface.
Overall, it was a very simple process.