Early on, my fleets are pretty small.
My current restarted game is Ion tech, though that was due to game setup rather than intent (went random for grins). My two battle fleets (more like squadrons) have 1xCG, 1xEscort cruiser, 1x heavy cruiser (railgun), 4xDDG, 2xES, 2xDD
Patrol groups are small right now, as I have no large colonies, so they run 3-4 FG or DD.
System defense is PDC and bases, along with groups of 1-4 FAC squadrons of 10xFAC.
Pretty dinky.
Even in my "big" fleet games, I dont think I ever had more than 20 to 30 ships in a fleet.