Suggestions for upsizing from ITX build for Proxmox server

A few years ago I built a mini ITX with these specs:

• cpu i7 10700
• gpu zotac twin edge 3060ti
• ram: 32gb ddr4
• Cooler: CoolerMaster MasterLiquid AIO 120mm
• MoBo: asrock H470M-ITX/ac
• PSU: Corsair Supernova 550w PSU
• Case: Sugo sg13
• some assortment of drive I don't recall 4.5tb total

Back then I thought I'd get some portability out of an ITX build but that wasn't the case, its still too heavy and fragile for me to feel comfortable lugging it around. I'm hardly getting any benefit from the small form factor, but still have all the downsides: poor upgradability, hard to clean, limited expansion.

I got a proper tower, phanteks p400, from a friend and plan to move my computer into it and gradually upgrade bits until it's a proper ATX system, ship of Theseus style, and eventually with the old parts have a solid HTPC.

I use this system as a proxmox server that I access remotely and don't generally use more than 2 vms at once for gaming, programing, machine learning, etc. resources are perfectly adequate for now, but I'm starting to run into the limits of the system and I'd like to consider an upgrade plan.

PSU is the obvious place to start, probably move up to an 850w unit or more.

Here is where I generally get stuck, should I:

• save up for a current gen mobo, cpu, ddr5 ram upgrade
• get a LGA1200 mobo for cheaper and still have the option to move to an i9 and get 2 more ddr4 dims for 64GB.
• something else entirely

GPU and storage aren't dependent on the mobo or cpu gen so those will be more based on need and when I can afford

So, I'd love to get some feedback and advice to make a more informed decision. Thanks in advanced