Logic board replacement software included for iOS?

I know first off that replacing the logic board to simply upgrade the flash size is a waist of money because its not that much cheaper then to just purchase another iPhone with larger storage. Now that being said I want to because I feel like it and it's fun and I enjoy a challenge. I am trying to figure out the best place to purchase a replacement logic board for this iPhone 5 16GB model with a 64GB model for AT&T, does anyone have any suggestions? Now the other question, do the logic boards you purchase come with the operating system pre-installed and if not how do I go about doing this? Any help would be greatly appreciated. I am an Android user mainly and I understand how to do all the software and hardware on that platform but Apple is a new platform for me.

Thanks!