How many do you really need? If the system is up and running with only upgrades planned for the future, you could get by with a couple of SA and BA people and a DBA. The DBA could be shared with other applications of thd DB. If your IT group takes care of the hardware and system backups, that reduces a lot of your SA load.
If you are in a developing or customizing environment, then you may need some additional resources, notably programmers to do the customizations.
What do you see as the needs are for SA/BA people? What tasks will they be performing on a daily/weekly basis that would require multiple people?