ZFS3-2 planning questions

Hello,

I have some planning questions for ZFS3-2 with 2 controllers(on each 2 read cache SSDs available) + DE2-24C(4 SSDs for log available):

Target is data integrity (RAIDZ2 intended) with best possible performance.

As we have no previous experience with ZFS3-2 or zfs in general, some questions arose:

1)is it wiser to put all HDDs on DE2-24C to new pool(RAIDZ2)at once or better make pool from half of disks to have option to grow pool later or even create other pool later?

Incentive to not put all HDDs at once is to have space for other raid options later in case this is too slow.