Dave, you might consider snagging a nice 500gb SSD to pop into that T510. i replaced the HD in my 10 yr old ASUS a while back. It was pretty easy, I have a SATA>USB external unit that had a drive failure. I simply pulled that drive out and installed a new 500g hard drive, then ran the cloning software that you get from Seagate, Samsung, etc. After that was finished I swapped the drives and everything came up, but with lots of empty storage space.
The T510 drive is really easy to replace, if its like the one I had at work a few years back.
I was just looking at a video about my S340 which has a 256G M2 SSD. It seems there's an empty SATA slot just waiting for a nice SSD data drive, so there's likely an upgrade in my future. 756GB should be plenty for a general use laptop.
... back to the OP:
With SD cards now readily available in 64 and 128GB sizes, that might be a prudent option, although reading from SD cards is never as fast as a true SSD. I don't know how well Cubase would run from an SD card, especially if he's used to the lightning fast SSD, but you could certainly move your data files there. Can any of you Apple folk comment on if its a major deal to upgrade an Apple to something like a 1TB SSD?