If you really want a 16ga - then that's what you should buy. You have to fulfill your dreams once in a while ...and if that's what it takes - go for it ..
But just to think this issue thru a little:
In your reasoning you mentioned you didn't want to load a 12ga down because you don't reload - and that's fine / but you can buy a lot of 12 ga loads these days at 1 oz - so you don't need to reload. There are all kinds of shells at 7/8 oz, 1 oz, etc in 12ga available these days ( at way less than 16ga ammo prices ).
You said you like a smaller receiver than a typical 12ga O/U - that's ok - I agree that a 12ga will often be almost a full pound heavier than a smaller gague receiver for a 16ga or 20ga. But since you're looking for a deal /or a good used gun - there are a lot more guns available in 20ga than you'll find in a 16ga especially in the Citori lineup. And for a 20ga you can buy a lot more shells in loads from 7/8 oz, 1 oz, 1 1/4 oz in 4's, 5, 6, 7 1/2, 8's or 9's ...... at a savings of at least 25% over 16ga ammo. It will also mean you'll be able to buy a lot of "promo" shells on sale - and practice at your local Skeet, Trap or Sporting Clays ranges with less expensive ammo than anything you can get in 16ga.
I think the Browning Citori Lightning series - or any of the Browning Citori's are fine guns ( I have a bunch of them ) --- but if a 20ga Citori will give you everything you want in a gun ( light, swings easy, a variety of shells available retail ), respectfully, I think a 20ga Citori Lightning, 20ga Citori XS Skeet, 20ga Citori 625 series, etc. - is a better buy for you.
A 20ga Citori will also be a better resale gun down the road / there are a lot more guys looking for a good used 20ga than there are for a 16ga - and mostly because of the cost of the shells. Unless you reload - shooting a 16ga is a pretty expensive option.