Forget to say that if your doing some big part like hood, you might wanna add to paint and primer that stuff which makes it more elastic so it doesnt crack, dont know the real name.
There is also plastic/fibre glass adhesive.
This starts to sound expensive and difficult ...
...its not.
Ask from car paint shop, they normaly give good advices , assuming that worker there isnt one of those "I dont know, Im just working here" types.