Cres island by Bicycle on Car ferry

1.  Yes, you can take bicycles on the roof of your car on the local car ferry – here is a topic with more details: https://www.croatiaferries.com/topic/bicycles-on-the-car-car-ferries-in-croatia/
2. Perhaps Valbiska to Merag ferry is the most suitable option for you. Here is a map:
   https://www.croatiaferries.com/maps/north-adriatic-local-ferry-map/

So, drive from Plitvice Lakes to Krk Island (riding across the bridge – no ferry needed) and take a car ferry from Valbiska to Merag on Cres Island https://www.croatiaferries.com/valbiska-merag-ferry.htm