Not in response to your question, but I recall being told that how one prepares the surface, if necessary, is very important. Are your walls dirty etc. Take care of that first. Does it need sanding to get rid of rough spots? Use masking tape around windows, baseboards if not the same color, the border** between the wall and the ceiling, unless you plan to repaint the whole ceiling, not the crummmy 3/4" tan stuff but I think the better stuff is 2" and blue. There's even wider stuff, sort of like to make a petticoat, for certain situations but I can't rember what.
I painted all of the outside of my house and the open stairwell inside (which required using a ladder, two 2x4's, some plywood, and the second floor to make a scaffold, but that was long ago. I'm sure I'm forgetting things. Find some instructions.
**Many/most experienced, skilled painters dont' have to do this because they know how to paint a straight line, but i don't and no newbies do.