I guess you could use just one key for the whole thing, but generally, using the throwaway key keeps you well used keys open for modifiers ( have shift 1 and ctrl 1 bound to other things) and solves a few macro limitations. For instance, my follow macro is just one button, but to start it, it has a stopmacro line:

/stopmacro [nomod]
/target [blahblah]
/follow
/cleartarget

so when I hit it on the current window, it does nothing. Now you could modify all your macros to work like this:

/cast [nomod] Lightning Bolt
/stopmacro [nomod]
/target blabblah =rest of normal macro

but I find there's very little room for it. I'm maxing out the 250whatever character limit every time, every macro. And from personal experience, it tends to do screwy things when you don't put it in the stopmacro part.

As far as # of macros, I only have 6 ftl macros, taking up 11 keys . Q=follow, bound to itself, F=assist paired with [, 1+comma, 2+period, 3+semicolon, and 4+quote are all attack keys. The rest of the keyboard is free to operate as normal. I have plenty of other keys bound to abilities too, but to use them, I have to tap the assist key to make sure they're all on the same target, not any different than a regular focus or named lead setup. But for grinding through mobs, often my slaves don't have anything targeted.

WTB, keyclone needs an override keymaps to go alongside his override Roundrobin and Donotpass