1. There is no difference what aircraft you have. All parameters are universal for any plane, it doesn't matter if it is b737, or B58, and you don't need to stick with some specific the developer brand (as FF or others)..
2. LOC = NAV
So, the parameter for the button is AP_NAV
3. See in the AP layout map - "NAV/HSI course select display.
Frequency for ILS? It is NAV1 frequency.