This is really helpful thank you so much 
I think I got it now. So zfs is really smart and the record size that you choose is an absolute maximum. Zfs will check what size is needed per file. For example, if you create a 4 KB text file, ZFS will store that in a 4 KB record. If you create a 12 KB text file, ZFS will store that in a 16 KB record. If you create a 720 KB text file, ZFS will store that in a 1 MB record. Etc.
That’s why lz4 compression is really cool.
I will run with:
1mb recordsize, and lz4 compression. Still waiting on my hardware to get delivered so plenty of time to work everything out