That's up to Tony.
For the most part, SFU scenarios have set Order of Battle (OoB) lists. This accomplishes a few things:
-- With any luck and skill, the OoB sets a good game balance. Yes, using point-values does, too, in theory, and many SFB/FedCmdr scenarios say "select 'X' amount of ships" to get there. I tried to calculate the total points on each side to give both a fighting chance to win (no pun intended).
-- It sets up a historical scene, usually to coincide with a fiction story and/or to fill in the grand scheme of the SFU timeline. This scenario was originally intended to do both, but the companion story has been "overcome by events". I tried to set a reasonably historically-accurate mix of big & small ships in each fleet.
-- It forces players to use ships they would not otherwise select. This is especially important in FedCmdr & ACTA more so than in SFB because SFB uses a Year In Service data to say what ships are available. This scenario was originally set twelve years before the start of the General War (aka the Great Galactic War), so a lot of ships were simply not invented yet. Even with moving to the later date, ships such as the BCG/BCJ and C7 are still not in service yet.
-- It helps prevent min-maxing / meta-gaming, or as a friend of mine likes to call it, "cheating within the rules." I didn't want one side to cash in half their heavy cruisers fo a dozen frigates, for example, to gain a lot of Inititive sinks. But nobody here would do that, right?
-- It'll help Tony with set-up time because he can have all the pre-selected ships ready to go ahead of time, rather than waiting for the players to decide at the last minute how "best" to spend 'X' amount of points to build the ultimate fleet.