Interesting tour! I travelled most part of your project, last year the Krym coming from Georgia, in 2009 the Danube from Budapest to Tulcea and the Black Sea. The Danube is phantastic landscape and friendly people. I would recommend to choose the southern side of the river from Tulcea (with a visit of Galati on the northern side) and thus visit the whole Bulgarian side and the Serbian side up to Ram (Serbia). There are more hills, but its worth the effort!
Have a good trip!
Paarios (Switzerland)

you may take a look on some pictures
Danube: https://picasaweb.google.com/100936285236581376857/Donau2009#
Krim:https://picasaweb.google.com/100936285236581376857/2011SchwarzesMeer3UkraineKrim#