You cannot,
So, you may use this node for tests, especially for filewalker.
I do not think so. You may use ext4 and will get acceptable results, and it can be used on Raspberry Pi starting from model 2 (see Can Storj run on a Raspberry Pi 2? - #2 by ipoli800).
But perhaps on top of LVM to make your life a little bit easier when you would decide to move this node to a bigger drive. And this combination should have less impact on performance and memory usage in comparison with a single drive zfs.