Sure. You can mix them. Why would you? It will not help prime the walls or wood. The primer coat needs to be applied separately to be effective.
It is not necessary to use a primer for interior walls, but using one helps with adhesion and smoothness of the paint.
Apply a coat of exterior paint over the interior paint to protect the finish and to discourage mildew growth on the paint film.
It is best to use an exterior primer outside, rather than an interior. While, the interior paint will work, it does not have the same protection such as UV protection, and fungicide protection that is found in exterior paints.
Only if the 'flat paint' is water based too.
No and yes it depends
Either oil or latex primer can be used over interior latex paint.
No, it is not recommended to mix primer and paint together as it can affect the quality and finish of the paint job. It is best to use primer as a base coat before applying paint.
Yes you can.
It is not necessary to use a primer for interior walls, but using one helps with adhesion and smoothness of the paint.
Apply a coat of exterior paint over the interior paint to protect the finish and to discourage mildew growth on the paint film.
It is best to use an exterior primer outside, rather than an interior. While, the interior paint will work, it does not have the same protection such as UV protection, and fungicide protection that is found in exterior paints.
Only if the 'flat paint' is water based too.
Yes, it is possible to mix primer with paint. This can help improve the coverage and adhesion of the paint, especially on surfaces that are difficult to paint. However, it is important to follow the manufacturer's instructions and test the mixture on a small area before applying it to the entire surface.
No and yes it depends
I wouldn't. I don't think they would have called it "interior paint " just for fun.
You do NOT use regular paint as primer. It contains none of the qualities of primer.
Latex primer is undoubtedly the quickest drying paint.