I don't currently play or buy any TCG cards so this is just generic advice.
- Set limits on what you're willing to buy/spend/etc.
Prices on this stuff can change with the wind and cards that are new, popular, or seeing competitive play will come at a premium. Most TCGs offer reprints of valuable cards in stuff like structure decks and starter packs. While not the flashiest cards you can buy they'll get you the core parts of what you need to play.
- Think about how you might organize, store, and protect them now.
You're probably going to end up with tons of bulk to store and rares to protect. There are plenty of options to do these things but figuring it out before your house is full of cards is best. Cards that are worth almost nothing now can suddenly skyrocket in price if the meta changes, so keeping them around and in good condition is a good idea.
- AVOID MYSTERY PRODUCTS
Almost every TCG has some repackaging company pushing "Mystery Box" or similar style products. These are almost always repackaged bulk of sets they had a hard time selling and junk cards from starter decks. They're also targets of theft because they advertise rare cards and items so it isn't uncommon to buy one only to discover stuff is missing when you get it home. Don't fall for it.
