So I just took over the castle and I'm wondering how you can recruit minutemnen (not settlers) to the castle? If you can can you do it for other settlements too?

I dont want to fill the castle with settler named npc, perhaps a few, but I mainly want to be a base for an army not generic settlers.

The settlers technically ARE the minutemen. They're citizen soldiers and you can deck settlers out with combat armor and fat men if you want

The minute men missions, the farms you save agree to join the minute men. And the radio tower you activate is to help gather more.

I know, but still I'm wondering if you get more spawns like the ones you attacked the castle with, whom are named "Minuteman" and have minuteman outfits.

About the farms/settlement missions - Your just talking about those people in the settlements right ("settlers") I don't get "minuteman" npc's by completing the side missions, or?

Ah, so the radio tower is enough to increase the population in the castle. Good, because I was about to build a recrutiment beacon in the castle.

Radiotower hasnt increased the population in castle for me, so i think beacon wud be needed.