Instead of guessing about how large of a starter you need to make, use the calculation tool provided at yeastcalc.com
. If you have a stirplate, use those parameters. Be sure to put in the OG, batch size (going into fermenter) as well as the production information about the yeast. Then figure out what size starter(s) you should make to get the proper pitching level.
Also, if you only need a 2L or 3L starter, you can just make the one. If you don't have a flask large enough, then do two or three steps with the flask you have.