I was thinking of a Monk 8/ Paladin 12 combo with Refocus. Go Kensei for a non-rapier d8 weapon, like a battleaxe or longsword or whatever, but now using it as a DEX-based weapon instead of STR-based. Take Dueling Fighting Style for your Kensei weapon. You'll get to add improved divine smite on the Kensei weapon as well, but not your unarmed strikes (some might still debate this, but that is my take anyway). Regardless, you can add divine smite on any hit as well with 4/3/3 spell slots to use.
Assuming DEX 20:
Attack action (2d8+7 dmg)
Extra Attack (2d8+7)
Flurry of Blows (d6+5 x2) as bonus action (KI point)
Flurry of Blows (d6+5 x2) via Refocus (2 KI points)
Also, assuming you hit at least once, you can add your Kensei Deft Strike for an extra d6 by spending another KI point (3 points total).
So, say you hit with one weapon (2d8+7) and 3 FoB (d6+5 each), tacking on divine smite of +4d8 x3 and +3d8. Don't forget that extra d6 for Deft Strike. Average on 4 hits of 6 would be:
34 + 30 (includes Deft Strike) + 26.5 + 22 = 112.5 damage.
Not a bad nova IMO.
You can drop a couple levels to get Action Surge, of course, adding another 19-20 damage (assuming 60% hit probability) + any extra divine smites (you still have a couple 2nd level slots most likely, but if not there are 4 first level slots as well).
Oh, and if you have time and the right Oath, your CHA bonus (minimum +1, maybe better...) will make you more likely to hit with the kensei weapon... so slightly more damage there, too.
I'm sure there are better nova builds, but that was my thought today at work.
(Also, it is late after a 14-hour work day, my apologies if I messed up anywhere. I'm sure there's a good chance I did someplace.)
EDIT: So, this was supposed to post last night. Apparently I was so tired, I actually
didn't post it...