Starting collecting something that has been on the market for a quite while and is still bringing our new items is rather challenging. Especially if you are starting a bit late.
Luckily the collector fly has only bitten me for things I already had. It's nice to have at least something to start a collection, would be even more challenging to start from scratch.
But even of I had a good starting collection there are still many old things missing. The beauty of collecting such things is that it's not just walking (browsing) into a store and buying what you need, but hunting the items around the shops in good enough condition and reasonable price. For the new things you miss that part. Of course it makes it a bit more chaotic as you don't really want to focus on finishing just one part of your collection, but getting what you find.
The new things, while easier to acquire, is a different challenge. While you need to keep some budget available to catch those good finds from the older items there is always new things coming up you need to get before they go out of stock/print.
Doing both at the same time is the real challenge. It would be so much easier if either the list of items you want wouldn't be constantly growing with new items, or that there would be only a few nee items coming out every now and then you could just go and buy.