Two mounting/installation questions

There are no chassis holes but given its thin steel skin, drilling holes is easy. However pop open the cover before drilling to avoid blindly drilling and hitting something vital, like the ballast or the power leads! The power leads go directly into the ballast by some small push-connectors on the ballast. You have to tap into that connection path in whatever ways you want to. I.e., "improvise."

Yes, they can easily be flush mounted. You can also hard wire them with some modifications as they are designed to be plug in lights and come with a plug already attached the a 4' to 5' cord. However if you want to hard wire your lights with other lights this is not the best light for you to buy. You should buy lights designed to be hard wired not lights designed to be plugged in.

They can be flush mounted. They probably could be wired in series but check with an electrician to see how many or what is needed to keep breakers from flipping just to be sure

There are no knockouts in the metal wiring box so it would be difficult to hardwire w/o drilling your own connector holes..... Then it could be hardwired.... And of course in parallel (not series). Ceiling mounting is possible, as I said. You'd have to bugger own holes in the housing. You'd be better off buying another brand. Some are still made the old way. Lowes screwed up when their source for this nice little light changed the wiring procedures by dumbing it down with a plug in only.