Wow... that's quite some gear there. I would sell all these cameras except the 750D (none of them are particularly exciting except the 750D - you might want to keep that one) for - say - a 80D, and leave just three lenses: 10-18, 17-55 (I have a soft spot for that one...), 100 macro, and add a decent telephoto like - say - a 70-200/4 L IS. Much of your stuff is old one, so getting anything but small change for that might be a problem though... No idea wrt flashes; they may or may not be very important for your style. I make due with just one 430EX (first iteration - the "nuclear accelerator" one).
I can also confess to owning duplicate gear but some of it (the Tamron 70-300) is slowly getting turned over to my wife's control. However, I'm a firm believer in two body setup, especially since I'm shooting a lot in inclement weather - like today - where I'm always wary of changing lenses for fear of getting snow (that's what is being dished upon us these days) inside.
I can also confess to owning duplicate gear but some of it (the Tamron 70-300) is slowly getting turned over to my wife's control. However, I'm a firm believer in two body setup, especially since I'm shooting a lot in inclement weather - like today - where I'm always wary of changing lenses for fear of getting snow (that's what is being dished upon us these days) inside.