It is easy to get caught up in "what should I buy right now". I have found it easier to start with a Qube and the 2.5" strip and work from there. That said, it really depends on what types of patterns you lean towards. Scrappies are my new favorite, so the Qube works well. I have purchased several dies from Hancock when they were going out of business up here and like the fact I have some "specialty" ones that don't get used all that often for a low price. But I DO plan on going with more strips. Those can be subcut into all sorts of different squares and parallelograms (or however you spell that word!).
It really is all up to you. There is a Facebook page for people selling dies, but they go really fast (within minutes) of being posted. And to be honest, they are only $5 or so dollars off what you'd spend new. I'd go new. At least then you know the blades weren't bent from someone running it through their machine without the mat. Just my .02
It's fun, that's for sure!