It's not clear what you are asking. The GPT tables at the beginning and end of the disk are just partition tables. By default, they are 34 blocks long, but can vary. Those tables have no place to store boot code. That space is provided by a freebsd-boot partition.
To repeat what I've suggested elsewhere:
Make the freebsd-boot partition 512K, the largest size allowed. Why not? Boot code has grown in the past, and because of the next step, that space will not be used anyway. (The boot partition can be aligned to 4K blocks without penalty but also without any practical difference. Might as well, to be consistent.)
Start the first data partition at 1M for compatibility with non-FreeBSD systems.