@mitu
Thanks for the useful info! That's more than enough to get me on the way!
I've got ample general experience with Linux, I've even used some tools in the past that allowed my windoze to read (don't remember if also write) linux formatted media, but again I'm lazy nowadays so ...
I thought maybe Attract Mode would be fundamentally different from the normal retropie, but if it's fundamentally the same, then I already got my ROMS running from USB, and now that you told me that all artwork for Attract Mode can be scraped and stored on usb stick, I'll google around for the best scraping databases.
Got a Raspberry Pi 3B, but I'll soon buy a second one and that'll be a B+
Again thanks a lot!!!