I have an MPCNC instead of a LR2, but I think you can go a LOT faster in MDF. I documented a small speed test here: Maximum side load. At 2.75mm DOC I could go up to 64mm/sec. My steppers are not that powerful, and I was running them in series. Don’t be too afraid to try out higher feed rates in test pieces.
My understanding of chipload is that it’s the thickness of a single chip. If it’s too thin, your endmill is rubbing more than it’s cutting and things may get too hot.
Re 2) Yes, that can help. Also single flute instead of 2-flute can help.
Re 3) I’m not sure about the deep cut. I had more success with a shallower but faster cut. I could go up to 4kg according to FSWizard. (In practice I’d stay well below that.)
Re 6) If the connection breaks the Z motor will just keep on driving, yes. Until it skips steps or something breaks.
Re 7) There’s no good solution I’m aware of. Happened to me today, and left a nice hole in my material…
Disclaimer: I’m a bit of a beginner myself still… and my experience is on an MPCNC.