Hi there,
The requiremens look quite clear. Rather than relying on Access I suggest you to create a program utilizing an embedded database(db). In this scenario, you don't have to deal with the db directly. The application will expose the features you need via a simple UI and drive the embedded db in the background.
You mention that there'll be as much as 400,000+ rows but I don't know yet what each row composed of like how many fields are there, how long, its type, ect. We have several options for embedded db but it's better if we pick one after I take a look at your current db and possibly running some small tests on it. That'd also depend on your performance expectations like how quick would be quick enough for you, e.g for filtering - 1 sec. , 5 sec., ect.
Excel formulas feature is another story. Obviously, we can't simply transfer the data into excel and apply the formulas, that'd be terribly slow. If there was only predefined formulas, not to be amended later, things'd be rather easy. To make that possible the program should at least understand a subset of excel formula directives. If there're not many you plan to use and/or the formulas are not too complex that's doable otherwise not, at least not within the scope of this project.
No need to mention other requirements, it's all good and straightforward. I am planning to create this as a winforms application using c# to implement and expect this to take 15 days, thanks.