Rogue doesn't get the extra attack, and only has 1 bonus action, so at most it would be 2 attacks, no? Thieves don't have any kind of extra attack of bonus action or nothing: https://roll20.net/compendium/dnd5e/Thief#content
If you're using Tasha's then Gunner and Dedicated Weapon let you grab a musket. If your DM lets you use Focused Aim even on attacks you might hit with then it can trigger Ki Fueled Attack easily. It's passable damage plus being ranged means you can take advantage of Monk's mobility to actually skirmish and take cover as opposed to being saddled with the bootleg ranged combat that is typical melee skirmishing in 5e.
i think my main gripe is that in 4e I was a whirling dervish of death by punches (spinning leopard maneuver), but with 5e now it’s just… thwap thwap thwap.