With an un-modded FO4 I had all the settlements possible except one in my first play through. It got to be too much to handle with all the radiant quest and settlement attack spam. I didn't have time to play the rest of the game at all.
I am on my fourth character and this time I am sticking to a limited amount of settlements I will be actively supporting even with a few mods to disable the radiant quest and settlement attacks. I am going to concentrate on Sanctuary as my main settlement. Red Rocket will be my base with just me and my companions, no settlers at all. Might move my base over to the Drive in once I unlock the perks to build crafting stations. I will add Greygarden but I will not build a settlement beacon. That place is fine as is with the bots running things. And finally the Castle with a beacon going so they can feed themselves. The only other might be the Slog so I have some where to send the Ghoul settlers, that might show up, to. The whole walking corpse look just gives me the creeps.
The rest are going to get helped out via their quests until I unlock the quest to get the Castle. Once that happens they are on their own. I will probably just salvage what I can at each and move the materials to my main base for my various building projects I have in mind.
I have a mod that makes it so artillery can fire across the whole map so there is no reason for me to try and support around 30 settlements just to have the option to build artillery in each one to cover the places that were out of range of the Castle.
The Brahman thing is odd. Most of my settlements end up with one or two. A few don't ever get any. I had one that had like eight or nine in one play through. It was funny watching them all fight over who got to the one bathtub I had placed for them.