Here is a brief description of my procedure -
I paint these while they are still attached to the sprue - small parts; any internal parts, especially for the cockpit; internal surfaces like wheel wells.
I just give them one coat as a primer/undercoat/base coat. This will be the appropriate interior colour or a general pale - medium grey. But I don't paint large areas of the model that can be done after assembly
I usually start with the cockpit, then do the other stages. As I remove parts from the sprue I prepare them by removing moulding lines & sprue attachment points. This will remove some of the paint, but there will be enough left as a very basic primer. This first coat of paint makes it easier to see where I have sanded, and if the part is OK to use
Remember to remove paint from any surfaces that will be glued
Then I start the assembly, painting properly as I go. You just have to learn from experience which parts will need painting early on, and which can be left till the sub assembly is complete.
Where parts have been glued, filled, and sanded I paint the joints with pale grey as this shows if the filling is good. Then lightly sand the paint, ready for the final painting
Continue till the model is complete then do the main painting
Search YouTube for 'Making Plastic Model Kits'. There are lots of videos, both general and for particular models. You will see how other modellers do their work
The International Plastic Modellers Society is a large association for people who make plastic kits. They are friendly and helpful. I suggest you contact them, and they will answer most of your questions.
In Belgium they are -
www.ipms.be
Have you actually made anything yet? Buy a cheap kit and get started. You can read, & watch for a long time, but the best way to learn is simply to do it! But meeting and talking to other modellers is very good as well!