This all depends on your budget and what type of storage you need. If you need lots of redundant storage then take a look at Synology, they have some really nice NAS units that you can connect via the Thunderbolt ports. You can grow a Synology drive over time as your needs change and your budget allows. You can set up a TimeCapsule partition to back up your internal storage, and if you set the Sinology up as a RAID then you will be protected from data loss should a single drive fail.
If you want fast storage externally then take a look at the SanDisk offerings, I have a couple of their SSDs that I use with FinalCut for small video edits or Motion to create moving content. These are for fast temporary storage, the finals are uploaded to iCloud for safe keeping.
As you have probably discovered, you can never have enough storage. Take a look at the Synology units, they have an 8 bay unit that looks like a large toaster on its side, you can purchase that with just a few drives filled and grow it over time. Just check that it supports Thunderbolt connections as well as Ethernet.