Aside from the obvious computer and subscription fees, the jump to 5 from 3 is marginal. You have more guys to gather up and more micromanagement when it comes to the details - banking, gearing etc but since you are doing it all at the same time and with the same /follow model (individual control of 3 is not really viable) then it would be almost the same as 3. The step from 2 to 3 is huge. The step from 3 to 5 is trivial in comparison - as long as you level them at the same time.