Can we start a build using our drones from something like the Star Lancer, then leave?

Yeah. Again, a yes answer. Yes, you can. So once you set the building in motion, you can go on, carry on, block off, and the drone will basically do its job while you're offline. And if the build finishes, the drone will then try to get back to its host or its mothership. And if the mothership or the host is not around anymore, it will self-destruct. And yeah, you need to get a new drone afterwards, but you will get a replacement if you use your Star Lancer, for example, by simply repairing the Star Lancer and then you get it replaced by this process.