Starting down the path in researching a PCC with a suppressor, for the ZF-5T, can you directly attach a suppressor to the threaded barrel, or does it need a host mount? Does a 9mm YHM Mini Phantom Q.D. Flash Hider work?

Depends on which model you get. Most of them have the 3 lug mount with 1/2x28 threads on the end. Pistol suppressors will come with a 1/2x28 piston(usually) if it's a 9mm model. Some are shipping with just a direct thread adapter (YHM R9)which is what you'd use for the MP5. If you want to utilize the 3 lug then you need to buy a can that has a 3 lug mount compatible with that particular can.

I used direct threads on my Zf5-K and an AAC TiRant.  Works fine

My Fullsize and K PTR both have yhm R9's. I have a Tirant on my evo for the last 8 years. R9 a great can and looks damn fine on mp5