So, my perspective is from playing it a LOT--I've put a ton of hours into playing it, so most of my understanding of the game (informing my decisions I'd made) is from my play-standpoint.
Generally I'd start by going for a 3-shift rotation based on how many booths I have at the time, aiming for 6, then 9, then 12, then 15, and finally 18, plus extras as needed for the back stage.
Only having six means you're getting stamina issues, you're probably not fielding a solid backstage Advertiser that's pushing your reputation gains up. Costs in scramble mode were built around that loop, and in normal mode, well, you can personalize costs there, so keeping in that field should be good.
With respect to the brokers, my usual playpattern was getting the first free one, letting her work, then putting in another, and so on. The cost of brokers are reduced by how many open slots you have, so one way to manage this cost is not to have a constant churn until you're drawing more than 25 per turn.