Alrighty lets see if I can remember all the questions!
I dont see a gasket with the float valve and seat. It should have a white nylon washer under it. Do not worry about the black o ring, you dont need it. The second gasket in the pics looks like the gasket for the nozzle. That little metal clip works with the float valve and seat. The small end clips on the head of the needle, the large end onto the float arm. Then when the level drops in the float bowl, the arm of the float pulls the needle off the seat. They used to have issues sticking, this, along with the rubber tip, helps prevent this.
For the pressure tank rebuild kit, it is easy to determine which one you need. The difference is between the primer buttons. If it is black plastic or metal. That is all you need to know to order.
When painting, be sure to use self etching primer BEFORE the paint. The paint will not stick to aluminum unless you do. Also remember, keep it clean!
Also to note, here is a free parts manual.
Vintage Evinrude Johnson Outboard Parts & Diagrams - Catalog ITEM_2833