Storage on a home server

I am just getting into setting up a home server. I recently purchased a used HP EliteDesk 800 G3 SFF computer with i5-7500 CPU. It came with a 256 NVMe SSD and a 1TB HDD. I checked with crystal disk info and both drives seem to be in good condition.

I am planning to set up Proxmox on it, spin up a debian virtual machine, and use docker compose for most of my applications. Before I get going, I want to make sure my hard drive storage is set up properly.

I plan to install Proxmox on the NVMe drive. I purchased a 4TB seagate barracuda HDD that I would like to have mirror the 1TB HDD that came with the computer for storage. My plan was to replace the 1TB drive once I approach 1TB in storage as it feels like a waste to just replace it now especially since I don't yet have that much data. Is this possible to do this with two different hard drive sizes? Can I simply replace the 1TB drive with another 4TB drive in the future if needed?

Thank you!

​