Replacing Rusty Seats - Questions ?

[71gold]

So have cut out the spotwelds and test fit one section of the seats .
Here are my questions.
Please see photos
1- I have shown proposed location for cutting the existing top Portion of the existing seats.
Plan to punch new panel and spot weld the new panel to the existing portion of the upper seat edge.
Is this a good plan?
2- I have shown 3 possible locations (1,2 & 3 in photo) to cut the vertical panel related to the new panel.
I am thinking this would be cut to create and make a pcontinuous weld between the panels where they would abut .
OR.....treat this much like the upper panel and punch the new panel and spot weld to portion of the existing vertical.
3- best tool/ fitting to make quicker work of leveling the cut out spot welds and also to make fresh metal of the existing before welding and other final finishes.

Thanks for assistance.
Frank