Excellent observations!
For future reference, I have a blog that you can find in the link under my avatar that has that video and a written step-by-step method to use to fill the carto and tank.
Something that I do is to put a wood toothpick into that air hole tube in the carto to avoid getting any juice in there (Getting juice in that tube can cause some flooding issues).
When filling the tank, you only want to put the cartomizer
half way into the
completely assembled tank (both caps on the tube), which allows room to fill it through the hole in the top cap. (Again, take care to not get more juice into the carto at this stage.) Then after filling the tank 80% full, you can push the cartomizer the rest of the way into the tank. Put the drip tip on.
Filling the tank with the cap off, like you did on your first attempt, causes too much pressure in the tank when you put the top cap on with a full tank of juice, resulting in too much juice going into the cartomizer, making it flood.