I would say between 50 and 60 drones. HQ-2 drones for the commander, Elite- 18 for 3 crisis suits team, Fast Attack- 36 for 3 drones squad of 12, Heavy- 6 if you tank HH or 12 to 18 if you take 6 to 9 Broadsides.
That is a lot of drones. The problem is that they have low leadership. So, if I would do, an heavy drones army at 1500 pts., I would take 2 commanders (drone controller) with drones and a unit of 12 drones. But it is about 300 pts. per unit when fully armed. If your are facing an hoard army that might be good but otherwise limited against vehicle.
I tried a commander (drone controller) and 8 marker drone with him. They were a really good support. Iridium armor kept the unit alive and my suits and tanks were extremely effective against one unit every turn, BS 5, no cover. BUT, If I was to do that again, I would probably just take 2 unit of 8-10 marker drone and forget about the commander joining in and put him with crisis suits instead.
Never take shield drones, You want them to shoot a lot or make the others shoot a lot better. Shield drone by themselves are not worth much. One or two might be great in a big unit, but don't take a unit of them.