Expanding EX4100 from 4x4TB in RAID 5

I want to plan ahead. I’m slowly moving my CD & DVD collection from the original discs to my EX 4100 running OS 5. Currently it is set up as RAID 5 with 4 x 4TG discs and is indicating a bit more than 4.5TB is free. (I’ve gone from vinyl to cassette to CD and have been collecting since 1968.) Reading a few other posts, I could conceivably hot swap drive 1 with a bigger drive, rebuild the RAID and be good to go. Then hot swap drive 2, rebuild, go; swap drive 3, rebuild, and go.I don’t believe I’d need to swap drive 4 for a larger unit. Or would I? As inexpensive as spinning rust is getting, plus being a helluva lot safer than SSD, it seems like the way to go.
Thank you.