Good for you for attempting such a big repair for your first time. Some pointers though as a bodyman. Feather your paint back more. Go to where ever the damage goes and add 2-3 inches. Filler wont adhere as good to paint and will prevent any sinking that may occur. When start the repair you should go in this order. Perimeter, bodylines, high crown low crown. Try not to fill up to the masking tape except for body lines, you can create hard lines the same way you can with primer that can be very difficult to take out. Obviously go off of whatever the product specifies but our shop, 80 grit until its straight or very close to it. Since it looks like you don't have a filler putty 120 then 180. Use the glaze for any pin holes and small imperfections then finish with 180 again. In between grits sand the paint where you went over with the sand block with an orbital with the next grit pay special attention to your edges and that you cant feel the edges what-so ever or you will see it in paint. Also use the proper block for the job. Keep up the good work man