Is the PN54 S1 good for gaming?

No. The Radeon 740M is integrated graphics, fine for video and light titles at low settings but not for modern games. A mini PC with a dedicated GPU is the better choice.

How much RAM can it take?

Up to 64 GB of DDR5. Some listings ship with as little as 4 GB, so check the configuration before buying and plan to add memory if needed.

Does it come with Wi-Fi?

Yes, Wi-Fi 7 (802.11be) and Bluetooth 5.4 are built in. Confirm the exact configuration with the seller, since barebone units vary.

What is a barebone mini PC?

It is a chassis with the motherboard, CPU and often storage, but memory and sometimes the drive may be missing or minimal. You finish the build yourself or buy a pre-configured version.

Can it drive two monitors?

Yes. It has one HDMI and one DisplayPort output, so two displays can run at once without an adapter.

Is it a good upgrade from an older mini PC?

If you mainly do office work, web browsing and media, yes: Wi-Fi 7, DDR5 and USB 3.2 Gen 2 are clear steps up. For CPU-heavy work, compare against Ryzen 5 or Ryzen 7 models first.