Purchase a good used O/U,...the stuff they make these days are of poor quality unless you have deep pockets.
Stay away from anything Turkish, the CZ, Yildiz and so on are not Trap guns,...they are very inexpensive field guns, not worth a nickle once purchased.
Purchase a used Citori Trap or a used Beretta 680/682 Trap gun,...these guns will out-live you and parts are readily available. These guns also retain their value quite well.
Keep your eyes open on the net for a Browning/Beretta,...be patient,...better to spend a couple hundred more on these then to have more/less Turkish crap you wish you never saw.
Really don't need chokes if you only plan to shoot Trap, but it's a bonus if the gun comes with tubes.
my two cents