Assume say 9000 foot to represent attrition and those detailed on other tasks, and a maximum of 2000 knights (or as few as 1300).
Assuming a ratio of 1:200, then there will be 45 bases of foot and 10 of knights.
Assume say 8000 foot and 800 knights. This gives 40 bases of foot and 4 of knights.
If the knight ratios are halved (units of 150-200 knights are mentioned), then this gives the Florentines between 13 and 20 bases of knights, and the Aretines 8 bases of knights.