Where can I find acrylic plates? The ones on eBay aren’t super thick.Yes, you need to use an acrylic plate as backing. Write each grit size on the side of the balsa that you are going to glue to the balsa. Then you can read which one is which, through the transparent acrylic. Use spray adhesive.
No need to shape it into the handle shape of a paddle strop. A rectangular 12x3 shape will feel fine in your hand.
Personally I would trim the 4 inch width down to 3 inches. Unless you have huge hands, 3 inches is more comfortable.
Trimming balsa is easy though. An exacto knife to create a deep cut, and then you can snap it over the edge of a bench.
You will receive 1 standard"Clear" acrylic sheet that is a nominal 1/4" thickness (approx.). We will normally just send out all uncut sheets without special instructions from you. We can even do different thicknesses (prices vary & material thicknesses are nominal).