For questions 2,3,4 I find Illustrator to be much better suited to the creation of each item (compasses, lines of l&l, scales) which I then import into ps and distort/modify further.

I believe inkscape is the opensource (?) approximation of Illustrator, but could be mistaken.

I believe that you can setup guides in PS to which you can snap lines/objects, but it would take a fair while to do for a full grid etc.