Tell us about yourself!
Sand residue can usually be blown out with a compressor, or a hair dryer.
Excellent! Just what I need for electronic circuit board assembly, fiddly soldering and Arduino stuff. I'm going to make mine with wing nuts on the stands so I can fold it flat when not on use.
Excellent! Also note that this type of plastic string will shrink somewhat when moderate heat is applied (too much, and it'll melt). So if you use some as a lashing or repair to bind a couple of items, running a heat gun close over it for a second or two, or holding it close to a campfire, will shrink the lashing really tight.