Yes
If it's the standard light gray primer it should be alright.
It is generally recommended to paint the trim first before painting the walls. This helps to create clean lines and makes it easier to paint the walls without worrying about getting paint on the trim.
cream
when i was younger my room was pretty, with 2 light green walls, and 2 light purple pink walls. right now i want to paint my room a very cream yellow for 3 of the walls, and the fourth a very dark navy blue. if i don't do that, I'm thinking about maybe a purple color, with navy blue stripes. mayyybe.
Any paint store or home center should be able to supply you with the paint that you seek.
You might choose to paint walls red to achieve a vibrant atmosphere in the room. Red is also a color that doesn't yellow easily so it lasts a long time.
White or a shade of light yellow would work well.
White.
It is generally recommended to paint the baseboards first before painting the walls in a room. This helps prevent any drips or splatters from getting on the freshly painted walls.
Orange
blue with yellow stripes
The mixing of red paint and yellow paint should yield orange so your pigments must be undergoing a chemical change (the molecule is breaking down and reforming)