Yes you can marinade your feta. It should keep for about a month. Heat the oil until just warm, add the herbs and allow to infuse. Allow to cool before adding the feta. Chopped chilli, peppers etc can also be used for extra colour, crushed garlic, and I don't see why spices couldn't be used for a completely different flavour.
I find that the harder feta seem to work better that the softer feta's.
Feta can be brined between 12-15%. Personally I find that 12 is better, as I don't like is too salty either. You can soak it in milk for a hour, to reduce the saltiness if you prefer. HTH