Yes you can.  Mac is notorious for putting the smallest SSD in their computers.   I bought an OWC Thunderbolt RAID system.  It houses 4 drives, that work as one FAST drive. Never had an issue with not being fast enough.  The benefit you can have is a huge amount of space (depending on the size you get) You can make aliases of data on your system drive, to move files to RAID  to free up more space.

I formatted the RAID  drive to RAID 5.. This uses one drive (of the four) as a ‘safety backup’.  You can retrieve ALL data if one of the drives goes down.  The SoftRAID system is extremely robust. It will give you plenty of time to repair any corruption.

I have two Thunderbay RAID systems for 7 years now.  Only had to replace one drive in 7 years.

Take into account your future plans.  Maybe you don’t need all that extra space.  Perhaps SSDs will come down in price in the future when a new technique is discovered.