Painting new parts, How do you prep new panels Options

[Cool914]

I am starting to weld in new restoration design parts (floors, inner long, out longs, clamshells, battery tray) but wondering what I need to do to them in terms of prepping them (they don't seem to be primed or anything). I have read many posts and understand what to do to treat, prep and paint rust areas but unclear on how to proceed in terms of prepping to weld, paint new parts.
Do I need to use a wire brush/sand to remove any finish/coating from them prior to welding? Do I need to then paint the entire panel with self etching weld thru primer and then weld, for the areas that will not be accessible (e.g. inside the longs, between the outer long and clamshell)? Do those painted surfaces need to be sealed with anything or just left as they are, I thought self etching primer could not be left unsealed? As you can tell I am a new welder(and painter).

I plan to paint everything with epoxy primer once I have the welding all done.

I am going to call restoration design tomorrow, just thought you all might be able to give me some guidance on best practice.

thanks