I like my 12g 870.
I've got the 28" bird barrel, and the 23" cantelevered rifled barrel.
It shoots good.

If you can handle a 12g, the 20 ought to be pretty sweet.
The pumps are always lighter then the semis, and with your short barrel, it should handle very nicely.

I believe the finish on the 870 express is parkerized. It does protect, bu tit only buys you time. Dry them off when they get wet, and store them properly in low humidity.

Enjoy your new gun.