As for your crouch toggling:
set toggle_crouch_on "+movedown; set toggle_crouch vstr toggle_crouch_off"
set toggle_crouch_off "-movedown; set toggle_crouch vstr toggle_crouch_on"
bind <keycode> "vstr toggle_crouch"
You get the idea. Basically, I guess this would work with every command that can be sustained (you can identify them with a look at the binds in your jaconfig.cfg: the sustainable commands are those with a plus sign in front of them).