See...it's easy innit?
Well done. I think it's much cleverer taping the loupe to a T mount than to the camera itself like I do. May have to work on that.
Re the aperture issue, I'd go for filters instead of reducing the aperture (but that's mainly cos I'm lazy). An ND filter is the best way to go, but you can use reds/yellows/oranges etc. if you're sticking with b/w film. I just hold them in front of the lens, no need to fix 'em with anything as your hand's already holding the end of the lens.
Some lovely shots there, BTW. I can't wait to see more.
Whoops, almost forgot. It's not a real home made lens unless you use loads of red tape; black tape doesn't draw enough attention.