Just looking around and felt I could at least offer some advice.
I have been duck/goose hunting since I was eight years old at multiple private clubs, public lands and day hunt impounds across the U.S. now for 30 years.
My daughter has now been joining me for 3 years and shoots a Montefeltro 20ga with 24" barrel. She has dowed numerous ducks and geese from 20 yards out to 40 yards and actually has not lost a duck yet (knock on wood).
There are two main myths leftover from old days about barrel length.
1. Higher velocity / Greater range (true a long time ago), false now.
Modern propellants will burn up by the end of a 24" barrel, I myself only use 26" barrels in automatics for the balance.
2. A longer sight plane will enable more accuracy and swing better.
This carries over from the days of double barrels. Remember that an automatic already has 5 inches of sight plane before the barrel whereas a double barrel does not. Meaning a 28" automatic has about as much sight plane as a 32-34" double barrel.
Check out sillosocks for a great bargain decoy...their standard one is their best overall.
Save the money on a new barrel over 24" and spend the money on quality shells.
You don't have to go all the way to the true Hevi-Shot, but Hevi-Metal #2's or BB's 3" 1 1/4 (my personal choice), Black Cloud #2's or the like in the middle of the road won't dissapoint.