Ferry....First if you are going to spend most of your time around St John's then take the ferry to Argentia. Our friends took the ferry last year with their 5th wheel / 2 adults. It cost around $1000 each way. When travelling around the island there will be lots of smaller ferries so be prepared. You need to book the ferry well ahead and decide if you would like a berth the crossing can be 12 to 14 hours. You are not allowed to be in your rig.
The other ferry is shorter and obviously less. You will have to drive to St Johns and there could be quite a few small ferries to take.
Yes you can find campgrounds with 50 amp. Again, book ahead. The campgrounds are a lot smaller.
I don't know about travelling with a bird. You would have to check with immigration and the Canada food inspection agency. It may depend on the type of bird. I am sure your bird has to be in quarantine for 90 days, meaning not be around any other birds. You will have to check with Atlantic Marine as far as the bird and ferries.
Time wise...July and August will be the most popular times for travel.
Once you have a plan on what you are doing in Newfoundland, how far you want to go etc. Then it will be easier to make arrangements and help you.
Remember...Newfoundland is a bit more remote than other provinces. You may have to drive a little further, a little slower. One thing to be very aware of is moose. There is a very large population and road accidents are usually serious and deadly.