Ganache is optional on cheesecakes. Many varieties of cheesecake are possible with many different fruit toppings and garnishes, of which ganache is only one.

Sure. If you use a chocolate ganache, I recommend serving it with fresh raspberries.

Ganache can be used to ice desserts, whipped into a frosting, or chilled and used as a truffle filling.

Ganache is chocolate and cream. White chocolate ganache will be made by melting white chocolate and then adding cream. This is likely to be a lot sweeter than average ganache (dark chocolate) as white chocolate is sweeter in general and contains less cocoa solids.

add thick cream to it