wouldn't charging for puppy in an ISO automatically breach GPL? It wouldn't matter what else was added to the GPL code inside the ISO, any GPL code in a software product makes the product (in this case the ISO) subject to GPL, this is the whole point of GPL
pre-installed puppies must overcome the objection that they are selling GPL code - so as someone said (Bigpup?) it can only be a fee for the blank USB key, plus the shipping cost, plus any wraparound services, plus any proprietary code (e.g. you might have something to link the puppy usb to windows*)
from what little I've seen of this idea so far this seems too much like those services that charge you £50 for a deed poll (change-of-name) when anyone can write out the words (like basically) "I hereby change my name to Puppy McPupperston and won't be called Jim anymore", and sign it, and it's legally effective.
The core of the proposition could be realised by telling people "Get USB key, Download Rufus, put ISO on USB", which is non-valuable. And to the extent that it's also non-marketable - at least people fall for the deed polls
If someone is incapable of burning an ISO, and I acknowledge many people may be, the proposition becomes "assisting people without mental capacity to access open source software" and then you're maybe starting to build a distro around accessibility. Puppy has a weakness around peripherals, so you might realise value from building bespoke plugins for those communication boards used in learning disabilities settings, or translating the help guides for puppy into pictograms (etc).
The partnership with Samsung for them to ship their product with a Linux distro based on GPL code distro seems iffy. The licensor breaches GPL if the arrangement reduces to profiting from GPL code, and the licensee risks any software in their product becoming subject to GPL by extension. (even blank USBs from these manufacturers often have some pre-installed driver, or a backup utility - pre-install puppy next to it and their IP is now under GPL). The legals on that for Samsung might exceed the market value. I'd suggest mocking up marketing materials for them is likely to breach their rights in most jurisdictions.
The education world has access to UN-subsidized offerings that a startup won't be able to match (e.g. Laptop for Every Child - why pay $50 for a USB with puppy when there are other Linuxes that come with an entire free laptop?). And they usually don't go for them and stick with Microsoft anyway, due to certain factors of doing business with the public sector that (again) a startup won't be able to match.
(* re. adding proprietary tools to a GPL distro this is legally non-trivial and it's to do with how distinct they are - the safe extreme is like selling the blank usb for $2, burning puppy onto it for free, and then offering those people to buy the proprietary stuff separately for $48. And you'd need to have some proprietary stuff before getting into that, not Clonezilla - Clonezilla's small print would need reading)
(Opinions in this post are not provided as legal advice)