First of all, congratulations on your new gun. I've been shooting 11-87s for years and currently own 2 of them. I'd recommend that you pull the major groups and thoroughly clean everything. I'd "deep clean" the barrel to remove the "gunk" that's present even in new from the factory barrels.
My guns shoot great patterns with 3" Hevi-13 "Bronze" shells with 2 oz. of #6 shot or #7 if that's legal in your area. There are many chokes out there that will do just fine. Everyone has a favorite and it's largely a matter of what you want to spend. It's really all about the internal geometry of the choke tube.
Whatever you choose, all my best to you this spring.
Thanks,
Clark