First of all, try to break your project into manageable pieces. I would think you want to build a module that lights up one 7-segment display (digit) and then from there build a two display driver to display a given number.
You can then focus on the counting. Depending on the frequency coming in, the strategy can be quite different. You can configure a timer/counter to count into tens of Mhz, or you can use input capture to go into a fraction of a hz. So think about what signal you are dealing with first.
Then you will need to understand your encoder. What kind of signal does it generate and if it requires decoding, etc.
It is doable, you just need to organize your thought process more.