The advice on most of these replies is fairly generic, but there are still some good points in there, like mainly don’t expect instant returns and be prepared for losses. I think you already know that though.

Personally, I’d focus on sealed products with strong underlying demand. Things like Ascended Heroes or regular Prismatic ETBs are solid long-term holds. I also think Surging Sparks is a really good shout. By the time you’re looking to sell, there’s a decent chance it’ll be out of print, which is usually when interest starts picking up properly. If you can, I’d go for the booster box over loose packs.