Firstly, I would like to commend you on actually doing things this way, I kind of miss the calculated approach on this forum as most of the decisions concerning drive design basically go the “mouth to mouth” sort of way… I do like this because that guy did like this and so on.
And now for slippage, this table you provided does not actually account for slippage, that depends on the looseness of the belt and the centrifugal force (rpm and diameter of the pulley being the major factors here). And the formulas for calculating that are rather big, im sure you can find them in some more serious belt drive design manuals.
In fact yes, since we are all running at high belt speeds (to be efficient you need to try and max out the motors rpm, which can easily reach 6k for 192kv), the actual torque our belts are rated for is less than we put through them, but it only impacts the lifetime of the belts. No wonder people (especially aggressive riders) need to change out their stripped belts rather often. And this table is most likely designed to calculate for some industry standard lifetime of x hours … If you look at the actual tensile strength of the belts its quite high.
I am sure no one has ever calculated their belt tension force around here
For your last question, I am a bit confused. What do you mean mounting eskate pulleys to a diy electric shaft? You mean the shaft of your diy motor ? (PICS PLEASE sounds really cool !! ) If so the of course … there is no specific eskate pulley, you can buy pulleys with no hole, you just need to bore it to the size of your shaft, or turn your shaft to the size of your pulley if you already have it. Mounting is possible in many ways… shrink fit with a bit of glue, keyways with circlips, setscrews (please, dont use setscrews, its cringey as hell, but seems very popular here for some reason)