Personally, if it was me, and I was using a good quality emulsion like 'dulux', I would still slightly thin the first coat.
You being a diyer, you are going to be a lot slower than someone who does it for a living, and when you do the whole ceiling you have to do it in one, you cant stop off at a corner like you can a wall.
So if its too thick, you will be labouring, and being slower in rolling or cuttin in, you might not get as good finish.
Even me as a professional, I still always slightly water down dulux, as I find the finsh much better.
And I am with Third eye on this one, dont even go there with the one coat stuff, unless you pour into a kettle and thinned down like I have done in the past, as it will drag on your walls, and go all gloopy, in short, its a fercking nightmare to work with.