Good questions! The free app (there's only one freemium app, actually), has all 3000 words built-in. We charge based on how many you swipe into your deck (i.e. you decide to actively learn). The app comes with a free deck size of 50, then you can increase that incrementally with in-app purchases.

There is a healthy mix of nouns, verbs, adjective, and adverbs.

There isn't currently anyway to add your own content outside of creating individual cards within the app. It's something that I'd like to get to (if people find the SRS system useful, I'd like people to do whatever they want with it).