A: Yes, that's what it's meant for. I use it with 1/4" drip line with inline emitters. You have to plug the end if you want uniform pressure through the entire length of the tube. They work very well.
A: Yes, it closes off the end.
A: Yes, that is what I used them for.
A: No. This is for sealing the holes made in the tubing. Usually where barbs had attached ancillary tubing or where a hole was made in the wrong place. I seal off the ends by folding about two inches of tubing back and securing it in place with wire.
A: Yes, that is what it does. I use them at the end of my 1/4 inch drip lines.
A: Some will leak so I found it better and easier to leave it in place and punch a new hole for the new line.
A: If using the type of drip line I have (1/4 inch line with holes every 6 inches), I think plugging all the drip holes would not be worth it and, would be labor intensive: cheaper and easier to just buy new line to put in your new emitters. While it might be possible to insert emitters in the factory holes, it might depend on how old the line is and, how brittle in addition to how big the factory holes are. you might by the emitter and try a few to see if it would work..
A: If I'm understanding your question correctly, you have emitter tubing installed? This is tubing with pressure compensating emitters pre-installed at regular intervals. I would not plug these holes (with goof plugs) or insert Xeri-Bug emitters into them. Instead, get distribution tubing (https://www.homedepot.com/p/Rain-Bird-1-2-in-x-100-ft-Distribution-Tubing-for-Drip-Irrigation-T63-100S/202078376) and snake it through your garden. Punch holes and insert your 1/4" Xeri-Bug emitters followed by tubing etc
A: No made to plug holes indrip tubing
A: No, these are for plugging the end of 1/4" drip tubing lines or for plugging holes within 1/2" drip tubing. Rain Bird offers a cap for spray nozzles that is model 1800CAPS.