white Supermatt, first two coats diluted to mist, is a very good prep for all new bare plaster. If the plaster is not new, so does not need to dry out, a white vinyl matt is fine, and more durable, but again dilute the first one or two mist coats with water, so it soaks in.
I find a small soft brush best for the final edges of feature walls and wall to ceiling. you can buy a special flat fitch if you want. Your roller will tend to scuff, but you can use that first, then damp sponge off any smudges, then run the brush down the line. The texture will be slightly different from the roller but nobody will notice.
You only need caulk if there is a crack. Use very little. The thicker it is the more likely to shrink and crack. On white surfaces you can use silicone which will not crack.
Masking tape I think will leave a ragged line and might pull off the paint.
Paint the ceiling first, then whatever colour most of the room is, and your feature last. Move the roller more slowly to avoid splatter, and have your damp sponge ready.