Yes this means 4 units of Winged Hussars.
Using either 2 or 3 of your bases would be fine. The rules use a flexible system based on the frontage of a unit. It is the same with the scenarios, the squares of multiples of the basic movement distance.
If you are using 3 bases of 40mm each then the BW, the basic movement distance, will be 60mm. This means that each square on the scenario maps will be 1 foot (30cm) square on the table. If you use 2 bases of 40mm then the BW will be 40mm and that means each scenario square will be 8" (20cm) square.
Because the system is flexible if I was you I would be tempted to use 3 bases = 1 unit for the smaller battles and 2 bases = 1 unit for the larger ones.