No restrictions, no limitations, no downsides
Metalcraft cards are the obvious choice
But if you dont want to go back to Kamigawa, please just find a plane you can populate with Samurai and Ninja and print that plane as an expansion or a Commander/Battlebond product
This is a great way to get drunk, but probably not the best activity to engage in with expensive Magic cards
With Izzet Sleeves you can double sleeve your cards without compromising on fit, shuffle feel or protection so your most valuable cards will stay in mint condition
Youre getting 30 Play Booster packs, and each pack includes 14 cards, with 14 cards Rare or higher, plus at least one Traditional Foil card in every pack