Congrats on the 870 Express!!!
They are awesome and so popular, it' s been said that " ...over the years
EVERYBODY has owned an 870 at one time or another." I have a lefty version of the 870 Express 12GA and I shoot everything out of it (#8 skeet loads, #00 Buck, and even the Remington Slugger rifled slugs).
The finish on the stock will be fine. It' s no biggie. Just restain it back. It will add character to the gun! You will have a ball with your 870 for many many years to come! I know an older guy who I go duck & goose hunting with, who has a 1956 Remington 870, and that old gun is still going strong. It' s beat up, scratched, dinged, but it is just as reliable as the first day it was made! [8D]
Good luck with it!
Butch