When the MIB talks about Arnold and the Maze, etc to random androids, how do they know what he is talking about? Is all that programmed into every host? Or is it secret code that Arnold hid in the hosts?

Unknown at this point. It could be Arnold's code, it could be Ford's code, or it could be Bernard's code...

Doesn't the company able to 'watch' everything and every moment in Westworld? Do they know MIB is looking for the maze? Shouldn't they see Maeve is drawing the hazmat suit men? See she's looking for that bullet in her body?

I think it's akin to a camera security system with some triggers. They could watch everyone but they'd need thousands of employees assigned to that task, yet it seems they only have a handful of employees monitoring the park so they are able to watch anything, but not everything and they use triggers to catch special events. If a host ends up leaving it's usual path without a guest for instance, this would trigger an alarm..

What was that giant machine Ford is controlling? A massive mining machine?

Yes, this kind of machinery exists today IRL.. Perhaps not of that exact scale (it looked much bigger than those I've seen before). It has a rotary "shovel" at the end of a mast that digs and sends the collected material down a conveyor to be disposed in trucks.