This far into the expansion I have found that most of my toons have about 22-26 followers, and thus some need to be deacctivated ( or assigned to buildings ). Therefore the last few weeks I have been purposely using the head hunters to search for specific building followers to have them sit on buildings rather than have them deactivated and I always get the follower bonus's.
Just food for thought for those wondering what they can do to make the most of the botbase currently.
This is not really accurate, to my knowledge:
You can have max 20/20 followers, including these, working inside buildings before reaching lvl 100 and upgrade Garrison + Barracks to Tier 3.
Then have 5 extra for maximum of 25/25 followers, including these, working inside buildings of course!
If you lack some profession followers, you must have missed some zone quest chains in the leveling zones, or you are still not 100!
Then you have one acceptable option if your inside its level - go for the profession follower you need in the quest zone, simply because you can do it right now, and it usually do not start from lvl 90, but bit higher.
Short list from what I do remember: JC/BS lvl 92 in start zones - SMV/FFR, Tailoring lvl 94 in Talador, Engineering/Inscription lvl 96 in Spires of Arak both. Skinning there is one in the SMV/FFR lvl 90, and another one in Nagrand, lvl 100, available on character level 99.
Most of these have separate profiles in the Profiles/Neutral section here.