Frustrated with inability to do body work!

Spent some time the last 2 nights working on the door. Here are some pics of what I am encountering. Not sure I am doing this correctly.
After the first layer of filler and as seen in the previous post I laid down a solid 6"-8" wide filler application. I tried not to get it to thick.
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Getting ready to sand some of this. I am sanding using an 11" block with 180 grit to start. Once I get it fairly smooth I switch to a 180 grit.
DSCN0019.JPG Below you can see where I am at after doing 3 coats and resand. Trying to use a different color each coat so I can see when i get tot the previous layer.
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Heres where I stopped for the night. It feels very good but I have to do a thin coat using a glazing putty? there are a few scratches that need filled. My question would be how thick do I apply the glaze and how do you tell how thick you are putting it on. how far above and below the previous filler do I apply the glaze. Trying to learn and do this the correct way.
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Thanks for any advice you can throw my way.
Rod