There's no such thing as "undetectable" bot activity. All you can do is keep your "suspicion threshold" low enough that their fraud prevention algos don't ban your accounts.
When you have so many accounts that share a large surface like the IP address, there will be patterns in your account activity that tie all of them together. Patterns that you can't control.
Social media websites log everything. So imagine you are running 100 accounts on one IP to follow random people. One of Insta's algorithms will be like:
"these 100 accounts are following abnormally high no of people outside of their social graph and they share the same IP, have the same language locale, and same webgl fingerprint. Must be a bot"
And your accounts get yeeted.
So yes, get more IPs if you want to be on the safer side. Idea is keep the accounts per IP ratio low enough.