57mm x 89mm card sleeves 110 Wyrmspan Compatible (57 x 57 Mm) ensuring your cards remain pristine for years to come 57x89 Card Sleeves - Etsy

You can have a creature with vigilance attack, then tap them to harmonize in the second main phase if they're still alive

PSA, CGC, or Beckett certified cards As previously mentioned, cards already certified by a recognized grading service offer considerable additional security

Dont know enough about the older T-Chinese cards to add them to the list, but you seem to have them on your list already

Beast, Hardheaded and Break both deal cleanly with opposing items, and can come in clutch in certain matchups

Price manipulation still happens with Japanese cards, and especially from American sellers on Ebay or Mercari, but its significantly harder to do for a few distinct reasons