For the wafer crumbs, you can crush the wafers using a food processor or a Ziploc and rolling pin.
Make sure your cream cheese is at room temperature, or it may leave lumps in the cheesecake mixture.
You can layer fresh banana slices over the crust before layering the banana cheesecake filling. Just remember that bananas will turn brown the longer they sit.
Wait until just before serving to slice the banana for garnishing. Bananas will turn brown if they are not used right away.