I think this might be the right solution for OP, especially since they don't seem to have had the "experience" I'm sure many of us have had with this "simple" operation. If you are going to do it, them it should be done using a live OS and a full offline system backup, otherwise its very easy to lose a lot of data this way.

However, symlinks like that can make things confusing really quickly. I would encourage anyone using them in this way to establish some easily checked rules and abide by them. For example, maybe you only use symlinks like this in a specific folder such as /home/expanded. You can still have multiple links there like /home/expanded/on5TBdrive or /home/expanded/onPrimarySSD, but it makes it easier to remember, find, and check those locations later.

When you need to know exactly where something is stored, verify a backup, or find data without the symlink, then you will appreciate a set of rules that helps you.