Was in the same boat last year when I picked up a 11-87 with a 24" barrel a week before the season opened and got on here and asked for help. I'm sure you will hear this a lot but it's for a reason , Federal HW #7 is going to be the shell of choice . Start looking now as they can be difficult to find ( seasonal run) and it just gets worse the closer you get to the season. Many choke options but I went with a Carlson's .575 and got good results . Good numbers in the 10 at 40 and not too rifle like closer in. All that being said , try lots of shell and choke options to see what suits you and your gun best as that is all the fun of it but this should give you a good starting point. Good luck and have fun with it...