That sounds heavy as fuck Sir. Would also mean a lot of upkeep.
Obviously heavier... but not that heavy. Each only weighs 1.5. So 3 will but you at 4.5, the same weight as the Elite Cav Shield (lighter than the Knightly Heater that many use).
But yeah, the upkeep sucks! Cause you may never pull out the 2nd or 3rd shield. I'd say play it by ear. If your buckler keeps getting broken easily, think about a 2nd. If both get broken easy, think about a 3rd. Or honestly at that point, just think about a different shield. Though I know they whole point of this build is to go buck & sword.
I've carried 2 before to nice effect. That second shield has saved me a few times. Never carried a 3rd.
But your best bet is to carry just one, and avoid axes when possible.