Croatia

I always feel more secure when I know where I'm going. I stayed at Pero's place in Dubrovnik that Rick recommends and loved it. Dubrovnik is fabulous!

The best places can fill up early, so it would be wise to book ahead if there are specific places you'd like to stay. Advance booking is essential for the park hotels at Plitvice. If you decide to book as you go, Atlas Travel (a Croatian travel company with offices throughout the country) offers room booking services. They usually have a binder containing pictures of the rooms and will show you on a map where they're located.

Yes, especially if you are going in high season.

On the islands, there are travel agencies located near the ferry dock which have big signs reading "Accommodations". You can bypass the crowds of locals holding signs and photos (which always unnerve me) and go to these agencies to pick out a room. They will generally call the owner to come pick you up. This would be the most economical (and easiest) way to find rooms on the islands, as many of these rooms are in sobes which have just one or two rooms and therefore have no web sites or reservation system.

Depends on where and when. Dubrovnik I would. Korcula I just went to the TI and they made a call and I stayed in someones converted garage. It was a pretty cool experience because we really had some language barriers, but we sat on her porch had a couple drinks and "talked" for an hour. My memory of that interaction is still vivid 5 years later.