Alll sounds good.....
No need to have a DVD or CD reader in the workstation to boot. If you ever need an optical drive you can buy an external USB-attached optical drive, and can even boot from it if you have BIOS set to boot from USB devices included in the listing there. Such external cases with SATA to USB bridge built in are inexpensive and can be handy to have around. I'd recommend attaching it to a rear USB2 port if you need to ever do that, for best compatibility.
I'll assume you know how to W10 Pro 64 activate from your W7Pro64 install..... you'll want to do a clean install after that, but once you have W10Pro64 activated on that Z600, from any drive you have running on it that is properly W7Pro64 activated then your BIOS UUID will be stored at the central MS servers and you won't need to feed it a COA license code for W10Pro64 ever again. You can find how to activate as an upgrade, still, by searching.
There is room for a DVD and a second available 5.25" bay is available next to it in the Z600. Finally, I've posted with details and pictures on how to install that HP USB3 card here.