First attempt at real bodywork. Tips?

I've done floor pans, trunk pan, drops, inner fenders and straight line quarter panels.etc. Where it's easier to get away with some beat to fit, paint to match. This is my first time doing something more difficult like rust r&r in an a-pillar. I'm trying to avoid pulling the dash and glass. Have removed the rust back to good metal.
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My first question is will a copper sheet between the dash and a-pillar protect me from welding the a-pillar to the dash? LOL
I'm thinking slow and easy, Keep everything nice and cool. Do a spot weld, let it cool really well. Do another. Inside patch first, work my way out. Weld thru primer will be used for sure. Here's my donor.
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Any comments or tips will be much appreciated!