Welcome!
Local Replication Tasks would be my go to
You cannot create a raidz1 from two disks and add third disk later. [1]
You could mirror the two drives and add two drives as another mirror later. This would put you at a higher space lost for redundancy though.
Otherwise you would need to destroy the pool and replicate everything again when you start with two disk and want to add a third for raidz1.
Also with only two disks your options are limited to creating a mirror now or a stripe.
I deliberately do not link the technical possibility here, given that OP is new to all of this. ↩︎