You might want to look at the Arctic Freezer 12 instead of the i2, it’ll be much quieter. The i2 was $9 when it was recommended, seems like the price has roughly doubled making it not as good of a deal.
Unraid is an entire NAS OS, not just a RAID level. In fact, it’s not RAID at all. It’s parity protected JBOD.
Your disks don’t have to all be the same size, you can add disks 1 by one, and there’s a ton of cool features for homelab use. It’s extremely flexible and easy to use, and there’s a lot of options for power users as well. Some people are put off by the cost, but most people find that it pays for itself very quickly.