Creating a small interaction network with mediocre content is essentially the same as joining an engagement group, and can leave a footprint if you’re not careful. These really need to be authentic accounts with amazing content, otherwise it’s not going to move the needle reach wise. If the content and engagement rates of your slave accounts are shit, you’re just not going to get enough reach out of it to grow your main.
However, if your goal is to build out a high quality network to grow with your main using cross-promotion etc., start with a manageable number and think about your resources (time, money).
Regardless, I would focus on ways to fully optimize your main account first, especially if that’s the end goal. Crafting super sharable content and captions, hitting 2-3/day post frequency, increasing follower engagement, feeding into the algorithm with with Reels, etc. You want to unlock the potential there, learn what works best, then apply to your other accounts. If the main isn’t dialed in first, any potential engagement is wasted.
Larger accounts can become pretty independent as well, so if you have high quality content and just need to hit Explore to get that extra reach, think about ways to quickly boost that main’s following. In the short-term, you may find that manually engaging with other accounts in your niche will translate to a higher and more authentic following for less time/money.