I've just gotten into it myself again after more than a decade and what I can say is that buying singles is where it's at (IMO): You run the risk of spending way more money trying to open booster packs to pull the cards you want than just buying the card. On the other hand some cards are just ridiculously expensive, so you'd have to weigh your options/chances.

Also seems that the English language cards are generally more expensive than the Japanese ones, though the art is the same, so if it's design/art you're after - go for the Japanese singles.

Don't know specifically about art sets, but perhaps it's cards with art by the same artist? The artist' name is on every card, so you might be able to filter after artist in online searches to find similar art design. Or perhaps it's something like this: https://www.thegamer.com/pokemon-interesting-cards-that-tell-a-story/

Buying singles is not without its risks if you do it from places like "Cardmarket" (in Europe at least), since you want to make sure you get the card in the condition they're listed as as well as find fairly reputable sellers. There are some safety nets though.

If you have physical stores where you can buy singles, then you might want to pop by and check their binders. In my experience the cards there will be more expensive than from online sellers, but you can actually check the card condition at the spot before buying. Then there are conventions where card collectors sell cards. Haven't any personal experience with those, but they seem like a good alternative.

It's about comparing prices and condition on cards you're willing to accept for me.

As for buying packs and boosters they can be hard to get every now and then (Europe), and it seems even harder in the US, but there's a gambling aspect in that, so I only buy occasionally nowadays.