As far as I’ve experiences GDevelop has trouble with dynamically generation, but outside of that everything is fair game and possible. So yes, I believe all of what you ask is doable.
PS. I’ve seen on the trello that a dialogue system is ready for the next release, so that may not be available just this second but it’s coming soon.
In case you mean in-app purchase to buy in-game items with real currency it is not possible.
Other than that, it should be fine. And yeah, a dialog system is coming soon that is going to be allow us to create very deep dialogs with multiple options to choose from similar to RPG Maker and other RPG engines. But even without that, it is possible to create dialogs but can be a little messy depends on how deep you want to take it but doable.