Dont know about postgame equipment, but my team had no trouble with the seeds (thanks to Hawkeye and Cacti).
Spoilers about a change from SD3: The forest that was next to the ancient city is gone. The ??? Seeds can be found once in nearly every Benevodan dungeon and can drop from high tier enemies. I dont know about high level since the enemies seen earlier in the game are still dropping Silver and Gold Seeds despite being level 50+, but the Bee Queen enemies in the Wander Woods dropped ??? fairly consistently. And Weapon/Armor seeds are now rolled into a low chance in Gold and a larger chance/exclusive drop from Rainbow.
It's weird to me in relation. The original? There's a good chance you'd finally be hitting L38 at the final Benevodons, but I hit 38 before I got to Sanctuary. Class changed at 48, beat final boss at 69. 20 to 25 hour game.
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"In my headcanon, some staffer saw Trump pull out his phone and start typing so they just Terry Tate Office Linebacker'd him out of his shoes." - FFD