i found j.b's graver mods to work very nicely gettin into tight spots doing hobos. with great care, one can facet them the same as can be done on the normal size gravers.
i' d go with a 20. or even larger. you'll likely be asked to do a few things where a heavier vise would be better. the heavier one will not likely cause a problem on smaller items. jmho as for the "knockoffs", they generally aren't worth the money. a used victor will serve well. then too, you...
i think most any .5 will work. a difference of a mm or two should not matter. ugly but use hot melt to affix the lens in place. i did such for my leica. don't use super glue; it can fog the lens!!!!!
yes. many moons ago. i had a .25" square file, no heel, about an 80 degree face ! needless to say, everything i cut was a perfect disaster. in my defense, i didn't know what i was doing. then there was the "meeks book".