I don't know your age or your build (how big you are) but I think you should consider a 12ga. As long as you can carry it and swing the gun without it feeling awkward, the 12 may be the better gauge for you. A Remington 870 pump capable of handling 3 inch shells could be a good choice. As for recoil, the heavier gun has less felt recoil and you don't have to load the big shells. There are some excellent (lead) 2 3/4" turkey loads out there, Winchester makes a couple and 6 shot is also a good shot size for turkey. The 12ga will also be better for waterfowl and eventually you can grow into using the heavier loads. You will also find a more diverse selection of shells for the 12ga, especially in waterfowl loads but turkey loads too. Again this is based on the assumption that you can comfortably handle a 12ga gun.
When you stated "improved choke" I assume you meant a special choke for turkey and not Improved cylinder choke which is a pretty open choke. You will need to pattern your gun and the full choke that comes with the gun may be good enough to do the job. Patterning can tell you what your max range is for your gun/choke/load combo and also where it is hitting in relation to your point of aim.
"Practical Turkey Hunting Strategies" by Ray Eye is an excellent book for beginning turkey hunters. It has a lot of good info in it and reading the book will give you a better understanding of how to hunt turkeys. The book can be obtained on the used market for probably less than $10 including shipping. Here is a link for the book at amazon.http://www.amazon.com/Practical-Turkey- ... 1585748757
As for the call...it would be better to get one soon and start practicing with it. Here is a deal for you. I have an old HS Strut slate call and striker I never use. It will produce serviceable yelps, clucks, and purrs. If you want it I will send it to you at no cost. Now I realize giving out personal information on the internet can be something you may not want to do, but if you can come up with an address that I can send it to its yours. A P.O. box or maybe your mom or dads work might work. Just check with your parents first and if its OK with them then PM me the info. Do not send me any info without your parents approval.