PDF-only computer?

Acrobat is not really a good tool for such tasks. Converting JPEG images to PDFs can be done using stand-alone tools, which are much more robust than Acrobat and can do it without visually displaying the file and in a much more automatic way (Acrobat requires user interaction, by design), which means that much less memory is used and the process can be much faster. The only issue is with the optimization. That's really something that mostly Acrobat can do. But if you don't 100% need that feature I would strongly recommend not doing it in Acrobat.

The graphics processor and its VRAM.

Some of the better rated brands of graphics cards are Nvidia GeForce and AMD Radeon.

And if you're looking for a system, consider gamers from Asus (the ROG series) and Dell (the Alienware series). Well-configured and reasonably priced. I buy these for our studio's graphic design workstations. Check Costco.com for good prices on basic builds.

The central processor and its RAM.

Look for the latest Intel iCore, which is now at its 10th Generation (but I don't see many 10s on the market yet). You want processor speed + generation.

Photoshop traditionally has run smoother when the computer's RAM has the same size RAM chip in each block. Example: 64 GB = two 32 GB or four 16 GB.