Kick plate is indeed the chassis plate.
I just priced copper and brass 20 ga. 6x10 plates at
onlinemetals.com, they were $16 and $12 respectively with $10 freight charge

2 things to watch with the mitre and tape:
1) No matter how I have cut the mitres, there are always some gaps; easy to fix by saving some sawdust and mixing it with a little white glue to make a paste and filling
2) I have switched from white or yellow carpenters glue to the dreaded polyurethane because butt mitres with the former just aren't strong enough to hold up when you plane and sand or, worse, try to chop or rout holes for plugs and such

Definitely chop all mortises before glue up.

Highly recommend cutting dadoes for splines to strengthen the joint