I have the Pro account and a lot of data there. I keep a lot of it (currently 392gb) available on my internal SSD (465gb net). I use SmartSync for older files/folders. However I am very near the limit of the internal drive. So, I have just added a 2nd 512gb (477gb net) SSD to the PC.
But what I'm learning from the site is that it's currently not possible to have more than one DB folder on a system within the same account. There should be a way to have more than one Dropbox folder (within one personal account) designated in the same system, for example on a 2nd/3rd internal (not intended to be portable) drive. Alternatively, having the ability for DB folder to span more than one physical drive would accomplish the same thing.