As for the number of bees per our hive: now (late summer) it is from about 50 000 (2 strong families) to 20 000 (younger ones).
It depends on season and apiarist decision, whether to enlarge family or not. The biggest numbers are in june/july. When autumn comes, the number of bees reduces to about 10 000 and by the end of winter the family should be almost of the same size (provided, that there was nothing wrong inside the hive: no disease, no starvation, no abnormal moisture due to e.g. perforated roof, no disturbing bee existence by pests, like mice and so on). There is surely a small amount of dead bees (usually 2-3 handfuls) - but it is normal.
The number of bees per hive also depends on hive type.
Some "apiarists" (not in Poland) approach in such way, that they get the whole honey in the late summer, and then bee family is free - guess, whether it manages to rebuild their stocks to survive winter!
Such "bee kepers" simply assume they'll buy young ones in the spring - and repeat the cycle. BUT IT IS NOT BEE KEEPING - IT IS CONTROLLED EXTERMINATION.