no won't be a problem but applying a soft sheen you have to be careful of picture framing where your cutting in will be different texture to roller so you can either use a 4inch roller of same fabric to go over while your cutting in or roll with your bigger roller as close you can to the edge over cutting in

There's no problem at all putting on soft sheen as the third coat. As long as it's had a watered down white emulsion miss coat and a second coat of matt emulsion then it should be absolutely fine.

as long as they are both water based paints i cant see any problems,
give at least 16-20 hrs between coats.

I can't see a problem with this, but bear in mind the plaster will still be very absorbent even after the mist coat, so ease the paint with some water( should have this info on the tin)

Hi,
As long as you apply a mist coat ( contract matt), to new plaster first it will be fine, though there is no need at all to then put a vinyl matt before the soft sheen. Your better off putting 2 coats of soft sheen on top of your mist coat as the soft sheen will need 2 coats anyway. Hope this helps,
Regards
Jonny

I would recommend that you still put 2 coats of the soft sheen on

你应该两个仍然适用coats of soft sheen paint.