I wish Adobe sold modernized older versions of Photoshop. For most of my uses PS 7 or CS1 is entirely adequate and those versions ran great on a paltry 400Mhz PowerPC G3 with 128MB of RAM, meaning that it'd be blazing fast on the cheapest modern laptops you can find.
Practically speaking yes, and it’s probably ok to do that for personal use. Where things get shaky is if you want to use it professionally — even if you buy an old license key off of eBay Adobe could decide the license is no longer valid and sue you.
If you had already that license I don't think Adobe can revoke it. I don't think it is legal to revoke a license that is sold in the second hand market either.
The biggest risk I can think of is that the old product may be in some case vulnerable to compromised documents and by sharing the sandbox folder with your main computer you could in theory get the main machine compromised.
Yes, certainly, but the article seems to imply that the author solved those Photoshop problems by creating a Web-based tool, while the actual solution is to make a lightweight tool.