They'll need some major shenanigans to make the invasion of the Human World seem remotely plausible. Unless they can repair themselves and have the logistics to supply themselves with all the high tech shit to maintain and build robots its like what? 10k robots against all of Mankind and the robots have 19th century weaponry and no knowledge of modern society.
What do you think the importance of Abernathy is?
We don't know enough yet to say for certain but if the Hosts control the park then they control the ability to make more of themselves. We just saw a drone version for the first time as well so it may be possible to make more and quicker since you don't need the full story line for them. They certainly have knowledge of mankind, intimately so, therefore they know their enemy and Dolores clearly references this. The park also seemed well equipped with modern weaponry and I'm sure it wouldn't be hard to make more.
For Abernathy, Ford's trump card for 35 years was only he knew how to make robots seem lifelike. Maybe not in appearance but in function. So they loaded up Abernathy with all the core code and tried to smuggle him out in case Ford burned the whole thing down on his way out which he kind of did. Abernathy still has all that code in him. Keep in mind Bernard is not with Tessa Thompson when he wakes up on the beach so something happens to her in trying to get Abernathy.