Never get gaps in my top layers.
Just One advantage of printing hot. The plastic flows better, bonds better and gives stronger prints.

As far as calculations go - you're over thinking it. Leave extrusion multiplier at 1.
You should be able to adjust the rest with temperature and print speed.

And layers. I rarely use less than 3 layers and outlines.

never had an issue with gaps, but then I don't bugger about with settings that don't need messing with :-)

Mind you I also never bothered with calibration prints. You soon learn what your printer does or doesn't do and design accordingly.