@buster921
It is a CTO machine therefore its REAL specs is in your hand
https://support.hp.com/au-en/document/c05792790
Its mother board has
One PCIe x16 slot
One PCIe x1 slot
One M.2 socket 1, key A
One M.2 socket 3, key M
and you say it has Optane that means the M.2 slot above is already occupied. But you can disable Optane and replace it with a larger (capacity) for Windows and programs.
A1. Yes, you can move Windows and programs to new M.2 NVMe SSD drive,
https://www.quora.com/Can-you-replace-intel-optane-16GB-memory-with-SSD
A2. As mentioned above, you have to disable Optane and replace it wit a normal M.2 NVMe SSD drive
A3. Physically it is a standard 2280 (form factor) M.2 NVMe SSD. For capacity, it is your choice from 256GB to 2TB or even larger. For example
https://www.samsung.com/au/memory-storage/970-evo-nvme-m2-ssd/MZ-V7E2T0BW/
A4. You can use Crucial P2 series or Samsung 970 EVO series (see A3) or similar from other vendors.
Regards.
BH***
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