Pick "one" Coach ... who is a very good shooter, calm, easy going and can explain things in common logical sense. Someone who looks like they make the game really easy and consistantly shoots top scores - generally has things figured out. Stick with them for coaching. After you've shot say five or six flats of shells, regularly, at skeet, with good coaching, and you've got your scores up into the high teens or low twenties, with some good reliable advice, you may be ready for a stock alteration or two ! Don't do anything "permanent" in the way of stock fit until you've shot it "as modified" a bunch, and are sure it helps. Way to many "stock butchers" and "Frankenstocks" out there.
A couple of guys I know that are 6-6" and 6-8" use 15+ & 16" length of pulls. A best bud at 6-3" likes his right at 15.
At 6 even, mine are 14 -3/8" ... but it isn't only your height - you want the stock comfortable - neither bumping your nose with your thumb knuckle under recoil because it's too short, nor so long you cant mount the gun consistantly under actual shooting conditions, without getting it caught under your arm or hung up in your clothing.
Try and get some good advice from one of the consistantly top shooters.
Have a good look at the distance between his fingertips (when wrapped around the pistol grip) and his nose, when his gun is mounted and he's shooting. Generally, this distance will be some 2" to 3" or say, 2 to 3 "finger widths" for most people. Some good instruction and lots of practice in gun mounting and actual shooting will help.
It's those "damn crossers" that will help teach you how to swing a shotgun smoothly and follow through !!!! Great lessons to learn well . Enjoy, and shoot LOTS - that first 25 straight is only a few months away !