HI! Welcome to Mossberg Owners!!! Happy Birthday, the 590A1 would be an awesome gift!
I have the same model, I shoot clays, though not competitively. I do however bird hunt with it, during bird season there isnt a limit to the shells you can have loaded unless you overlap a waterfowl area too.
You would of course have to have the gun threaded for the chokes, but not too big a deal, I could easily see addin that at least!
I put a short length of pull stock on mine and shoot birds the same as I do when I practice targets as if it were home defense. The weight of the gun, the shorter stock and some barrel work have made it a pleasure to shoot!
So to answer your questions;
I think its a fine firearm, couldnt be happier with mine and would certainly recommend it.
While I dont do too much sport shooting, I shoot clays, target, pick off individual clays with 00 buck, and kill birds which go on the table and we eat em. Because theyre tasty. And it gets crazy looks when other people see me carrying it in the field. But who wants to be like everyone else anyway?