2 vdevs with 10 x 10TB drives in RAID-Z2 would give you around 150TB useable.

So you could do that with one vdev and 10 x 20TB disks, but you wouldn't have as good performance and 20TB disks take a long time to resilver if you have to replace one.

Pick yourself up an MD3060e and fill it with 12-16tb hgst SAS Drives. Pair them up as 4+2 or 8+2 raidz2 groups based on your risk tolerance and needs, and remember that no matter how small you prune your data, it will continue to grow. Make sure you have plenty of capacity to grow into. If you haven't got an accurate projection of your growth, then you should provision between two and ten times what you think you'll need, depending on how much growth capacity you have in your hardware, and then calculate your actual growth rate for future planning

If you need more HDD trays you can probably add additional 3.5" drive bays in the 5.25" slots using something like an IcyDock. I did that on my tower server to add 2.5" slots for SSDs, but similar ones exist for 3.5" drives.