Interesting question! Here a reference to the what I’m collecting. I won’t go into too much detail for Pikachu, since it was my first collection after returning. In short: I knew next to nothing about Pokémon cards and started by buying all cheap English Pikachu cards in stock on TrollAndToad on impulse; then I started delving into other languages; I came across Justin’s Pikachu collection and joined the Efour forum; and now I’m a Pikachu expert, haha.
After I was collecting Pikachu cards for about 2.5 years I also decided to collect Seviper in a similar matter, so let me explain the process of that one first. I started by making a checklist of all existing Seviper cards in all languages. After that I simply bought all cards I could find on TrollAndToad, CardMarket, eBay, and/or Yahoo Japan. And from there on I checked those same sources every few days/weeks for the missing cards. With these kind of collections time and searching for them on a weekly basis is the most important aspect. A lot of cards I now own I’ve only seen for sale 1-3 times in 5+ years. And they aren’t necessarily expensive or very rare. They simply aren’t put up for sale often. Especially some foreign (French, Italian, German, Spanish) Reverse Holo cards can take a long time to find. And it’s also important to have a middleman in some countries (depending on where you live of course). I right now have a middleman I could ask for help in Brazil (for Portuguese cards); the US; Australia; Germany; Japan; and Indonesia. In the past I also had a middleman in Russia and South Korean, although I’ve lost contact with them (unfortunately, since I’m missing some Korean Pikachu cards from the Sun & Moon era).
With a lot of my collections researching which cards are out there while making the checklist, and then purchasing all the cards, was simply all there was to it. I started and finished my National Index collection in a few months time. I started and mostly finished my Yu-Gi-Oh rarity collection (excluding some rare misprints) in halve a year time. I started and finished my English and Japanese exclusive Full Art Supporter collection in a few months.
This was mostly possible because I had saved money for a long period of time. Right now I’m not starting any more new collections (or at least, I’m going to try not to). My savings account went down last year despite having worked full time without other major expenses. I could easily afford it, but I can’t keep it up with how fast cards were releasing for Pikachu and how fast I was adding new collection goals myself. I’m content with my collections thus far, so I’m going to try and finish the ones I have (just 1 more Seviper card; 2 more sealed Moltres; a few more misprinted Yu-Gi-Oh rarity cards; gen 8 for the National Index collection. FA Supporter collection is already complete), and from that point onward 100% focus on Pikachu and keeping up with new releases for all the collections.
The only real strategy I use right now is not buying very expensive cards one after the other and make sure my savings account doesn’t go below X amount. I currently have a 3k USD card incoming, but although another card I really want is available for sale as well for a similar price, I’m not going to buy it until at least 2-3 months from now and my savings account is back up a bit again. (The card will most likely be long gone by then, and when it pops up again it might be 1k higher than now, but so be it.)
Greetz,
Quuador