+1 on suggesting you consider the gas gun. Much easier to get perfect fit with shim adjustable stocks you don't get with OU. I think 30" is perfect, and if you opt for 32" later you only need a barrel not a whole gun. For low recoil must be gas, not inertia operated and as mentioned there are many way to minimize recoil if still too much from adding weight to the gun, porting, to using 1 oz or 7/8 oz loads, etc. Plus 12 ga more available as already and usually cheaper as already mentioned. And my arguments are not really related to any performance comparison of the gauges. I will tell you for sure my Win 101 26" 20ga with target loads recoils way more than my Beretta 391 28" 12 ga with 1 1/8 target loads, the 101 is very light and therefore a great upland gun. But also doesn't' swing well on clays due to lack of weight.
Quick story for perspective, years ago I was a member of a clays only club. The gun racks had many Krieghoffs, Perazzi's, Kohler's, etc. (days before Ceasar G). Not only were they all each worth more than my car, none were mine. When sporting clays got big even the guys with tons of money got on the gas gun buss. Almost amazingly they then spent a lot of money on upgrades they didn't really need like custom stocks, crazy chokes, barrel work, etc. IMHO it really bugged them to shoot cheap guns better. For sure part of the issue in those days were the super long barrels typical of sporting OU were not very well balanced for clays which is not the case today. But also remember much like golf, the best may shoot a lot of OU's but often they also get their guns for free or with some kind of sponsorship assistance based on the brand. I think you could shoot for many years before you reach the limits of the gas gun.
In full disclosure it's been many years since I have been on a sporting course so I am not aware how important it is to have different chokes. I will tell you that when I competed I found not changing chokes to let me score better by focusing on the shot plan and execution not worrying about the choke. Typically where I shot light mod the whole way. The idea I could not break close fast targets with a tight choke was all in my head. It's as much about the shot string length (or arguably more about) than the pattern diameter.
Also +1 on recommendation to find a good coach. Missing clays can be very frustrating until you learn enough to realize what you did wrong since you don't really know high, low, behind, in front, etc. Knowing doesn't mean you will always do it right but when you learn what it should look like for me at least makes it so much more enjoyable.
Good luck.
YMMV
John.
