I assume I can have dinner in the lounge in DXB when I arrive, even though I am only flying out to DMM the following morning as long as I have an onward boarding pas?
Can only answer this one.
Although EK has no arrivals lounge, you can access the departure lounge just as if you were in transit (<24 hours until your DMM flight).
However, when you leave you are now in the wrong place, so have to make your way back through transit security, playing the "I got lost" card, and join the arrivals flow to arrivals immigration etc.
Sounds awkward, but many reports on here about it being done.