I have done a lot of riding in Europe and have in one way or another done both these routes you are thinking of. It has been three years since my last trip to be fair but I can't imagine that much has changed. I would forget about the dollars if I was you, Euro will be accepted most anywhere and is easily changed in any of the Eastern European Countries with a standard rate. The dollar will change constantly so you are never quite sure where you stand with it at the moment.

If you want to sail from Bari, Italy to Greece it couldn't be easier. Totally hassle free and loads of help on the ferry to secure your bike from other riders if you don't know what your doing, which I didn't. The language barrier is not a problem anywhere either but particularly in the Eastern European countries just learning even how to say please and thank you will make a huge difference to how you are treated. They really don't expect you to know any words so it's a good idea in my book.

No worries at border crossings either as there is none in the west and a quick flash of your passport in the new Euro states is enough. Once you hit Serbia, Bosnia, Romania and Bulgaria etc you will need proof of insurance only. A green card can be easily gotten from your insurance company at home for no extra charge I imagine and if there is some countries where they wont cover you eg, Serbia and Kosovo right now then it can be bought at the boarder.

If I can be of any help to you with anything just let me know. You'll have a blast.

PJ.