Ideally I would want about 1kg of biomedia for every 100 litres of water for a fully stocked aquarium. 75g of water is about 300 litres, so about 3kg biomedia in your aquarium.
Your filter has about 3.5 litre capacity. Take out some capacity for sponge, you are left with maybe 2 litres for biomedia. 1 litre of biomedia is about 1kg, so your filter by that metric is good for a 200 litre/ 50 gallon aquarium in a real life situation.
Another metric is that filters are typically good for about half their rating. Your filter is rated up to 400 litres, 100 gallons. So it's probably good for 200 litres/ 50 gallons.
These 2 different capacities tally up.
How much matrix did you actually get in your filter?
So, i wouldn't fully stock your aquarium, but if the filter is set up optimally you could stock it to the equivalent of a fully stocked 200 litre/ 50 gallon aquarium. While you might get away with a fully stocked 75g aquarium, it wont be as effective at dealing with any spikes that might occur and wont pick up detritus and remove it from the water as well. Your filter isn't massively undersized, but it could be better.
I'm not sure what the difference between floss and polishing pad is. I use floss as a polishing pad. If the floss/ polishing pad is last you will be trapping all the fine detritus with your biomedia, which will cause the pores to get clogged and make it less effective. You want the floss/ polishing media before the biomedia to remove this fine detritus before it gets to your biomedia. The advantage to having the floss/ polishing pad last is that it's easier to change, but your filtration won't work as effectively in that order.
The ideal order of media is sponge/ floss layers from most course to least course, then biomedia, then chemical media.