Thanks for all the advice, even if I kinda already had those in mind.

But while the topic's on sources, might as well share some good sources for promo/cover art I've found, for posterity:
The Video Game Art Archive blog
https://videogameartarchive.com/VGDensetsu on Twitter/Tumblr (
twitter.com/VGDensetsu,
https://vgdensetsu.tumblr.com/) (harder to sort through; sorted by artist, not game)
And for Sega stuff specifically:
Sega Retro/Sonic Retro
segaretro.org,
sonicretro.org (tons of scans, occasionally clean art/screens ripped from old FTP servers and press discs)
The official Sega Forever twitter (
https://twitter.com/SegaForever) has been posting super clean art on & off for the past few months.
Also,
Satakore.com for barcodes/game info.
And here's a cover I whipped up from some new finds:
Die Hard Arcade

(found the front art clean on Sega Forever, realized the inlay background was just a zoomed-in section of the same piece, and everything else fell into place!)