Only from my experience, if I understand your questions >
You can combine everything in one PC or not. If you don’t combine it all to one, mini can work, as long as response to netspace, response to plots is fast enough. If you don’t separate f(x)s on 2 or more PCs, use a better PC, as plotting it will detract from the farming function at times, esp. under heavy plot loads (multiple GUI threads or MadMax) and also drive responses when copying to HD storage.
I’ve had a network shared farming drives for drives being plotted whilst on my separate plotting PC. Eventually they get locally connected, but no issues in the meantime. Initially had a 1Gb wired network connecting them, but upgrade to 2.5Gb, then to 10Gb, just for fun. I don’t see any real response dif between them. Good luck!