I use very little sera and only do one wrap around the tube so that it still is fluffy. Remember that less is much better for allowing the juice to fill the wick.
I fill my spheroid with needles(sharp or blunt if I have too). If you can't get one into the side of the tube filled with wool than it is too much wool. Do not pack it, especially your first time. As you d more refills in the future, you can add a bit more each time so that you find your perfect size.
The more wool does not mean a longer lasting tank. If you are dripping the juice in your spheroid, unscrew the top portion of your Spheroid and look at your fluff, this will tell you how much of your fluff is getting juice which is a good indication of whether you need more or less fluff.