Choosing whether to paint a wall with a roller or brush depends on the result you want to achieve.
It must be said that painting with a brush makes it possible to obtain a perfectly smooth surface while using the roller you will always have an "orange peel" surface characteristic of the technique.
It is also true, however, that the roller is certainly more practical for large surfaces and ceilings thanks to the extension to be inserted into the handle.
How many "hands" to give
A good whitening must provide at least two coats of paint (hands) to be given after a few hours (read the instructions on the paint package) so that the surface dries.
If you then want to change from a strong color to a lighter one, it will be good to have at least three coats of paint, while if you refresh the color keeping the color a single pass may be sufficient.