Is it advisable to use a 5TB HDD for persistant multiboot, and can that be done with no data losing?

I want to create a multiboot USB, containing: Live GParted*, Ubuntu Studio, and Windows. It would ideally have persistant space.
I’d like to use my ADATA HD710pro 5TB HDD than buying a pendrive. At present, it has a single partition. 2.78TB of it are in use. I backup it monthly, but it would be quite annoying to format the partition and having to copy all the files back.

So, the first questions is:
By using an external HDD like this for multibooting, or even single-booting, would I risk about loss of data or OS malfunction?

If not:
I assume that I should create the partitions required for Gparted, Linux and Windows, and a NTFS storage partition. AFAIK it’s preferable to keep boot and OS partitions at first positions in the disk. Can I just resize the current unique partition, leaving free space before it, with no data losing, then creating new partitions in that space and installing software on them?

*Live Gparted is not really necessary, as I can use its KDE alternative from Ubuntu Studio, having a Live version is just meant to being able to access it faster.