Ebike power monitor/controller

Hi
I am brand new to the Arduino though I was a C programmer back before windows.
I have an idea for a project to help control the riding of an ebike, I want to finally have it put onto an Arduino Nano but for prototyping work I want to use an Arduino mega.
A lot of ebike users will say why not use a cycle analyst, that device has many of the things I want plus a lot I don’t for this application I want to first fit it to an ebike that looks like a petrol scooter, these already come with a built in dashboard but in my opinion lacks certain useful things.
At the moment I am not sure how many I/O portals I will need in total ido know I will require one analog input and one analog output.
My first objective is to be able to get the Arduino to recognise the pulses coming from the hall sensor output from the ebikes controller be able to store basic information on the Arduino inputed from a two button keyboard like a simple cycle computer.
Kendrick