Which machine for old demos + HD + wifi + eventually linux?

[MskoDestny]

And there are also later demos that require faster processors and AGA.

If you want to run Linux, you really need to get an accelerator that allows you to add more than 16MB of Fast RAM. You also need at least an 020 (with a PMU and FPU) though an 040 or 060 are highly recommended.

Overall though it behaves just like linux on the PC (just slower). I don't know if it's really worth it.

[MskoDestny]

Well an A2000 will be fine for running demos. Slap a SCSI card in it and it can support hard drives(small ones). Proper large drive support requires one of the later 3.X versions which require at least an 020 though you might be able to "cheat" using on of the alternative file systems. Not sure on that.

As for WiFi, the closest you'll get is a standard ethernet card paired with one of those WiFi bridges. There aren't any WiFi drivers for the Amiga to my knowledge.

EDIT: OS4 requires a PowerPC accelerator and last I checked it was unclear when the version for PowerPC accelerated classic Amigas was coming out.