It's hard to try to answer this question, as I don't know anything about your approach to the situation.
If you think to keep account info and/or transaction info within Memento libraries, how do you plan to do that? In theory, you could use the Memento JavaScript Http object and related objects to script the accounts & transactions themselves and maybe fetch information from them into libraries or use the Zapier app to interface Memento with your banking app. You could build overview screens & reports using libraries and maybe JasperSoft Reports. JavaScript scripting could help automate some of the process and smooth over the edges.
What is your approach? What are your objectives? How will you know when you'll have it all done the way you want it?