No methods metntioned will make you money on one off plaques of 20" sq if you sell at those prices. You want at least 5x material costs as a selling price leat alone labour. You might as well just do it in perspex and paint it to look like bronze.
Google "Faux bronze" for precise instructions how to do the paint finishes.
In terms of etching , ferric chloride is nothing like as dangerous as acids , in all likelyhood the only problems you might have are staining your hands and clothes orange.
If you do master Etching, you will have a lot of other applications for it , like doing stainless steel etc.

the resell should be around $60.

I think that if I am producing 50 -100 per week my labor cost will not be so high. I am guessing that my material cost should be around $5

I can't remember how long it took to engrave the small piece in the photo. I know I had to run it three times with my 30-watt laser to get a reasonable depth. I actually should have run it one more time.

A higher-powered laser is the tool for this substrate. Routing may also be okay if fine detail is not required.