I think the scientists were Hosts. I'm 100 percent certain of it. That would be the only way that Ford would be certain about Maeve and putting her on the path to her choice.
I'm not so sure that Felix is a host, he has a certain inimitable presence: a mix of fear, intrigue, and incompetence; too many emotions to be replicated via code. For as human as the hosts are, they can't replicate all human dynamics, case the subtle differences between Arnold and Bernard.
Regarding Delos' main play, I think it is definitely uploading human consciousness into a host or some after life reserve to visit lost ones.
Which would lend to the theory that the Ford we saw killed was either a host or Ford already uploaded his conscience into a host.
Creatively I could see HBO making it into the latter in the event Anthony Hopkins is too pricey to bring back they can say Ford uploaded his conscience into a younger version of himself or shit another body.