Well, good luck to you but you're competing in a very crowded field. Disconnected expense-tracking apps are just one step under Todo apps, in terms of number of alternatives... And most users just don't stick with them, because manually tracking every transaction is exhausting.

When you'll start thinking about adding automated bank fees, which is the necessary progression of the concept, then you'll discover why there are so few "connected" versions compared to the plethora of disconnected ones.