Dear Barb,
It sounds like a great plan you're putting together there. I highly support the guide's choices, too, as she is the local expert in the end. However, I want to make a suggestion. Since you are spending 4 nights in Sibiu, why not enjoy both areas and have 2 day trips or a day and a half, as Marginimea Sibiului is easier to get to?
On the other hand, the Romanian countryside is so diverse and different from one region to another. You will see that in September and agree with me. I'll shortly give here some examples as others might be interested in this subject.
Romania has 9 major historical regions, with their own traditions, crafts, folklore, food and architecture. Romanians speak the same language no matter the region, but local accents and several regional words differ. Also, these regions were part of or under the sphere of influence of different empires, which left their mark on all aspects of life - from language and food to the layout of the villages and the way the houses were built.
. I'll list based on their fame abroad, not on their importance or beauty:
- Transylvania - part of the Hungarian and Austro-Hungarian Empire until WW1, hence the mix of German and Hungarian communities all over the region. Not to mention the deep German (Saxon) influence that shaped all the medieval villages and towns so popular now among tourists coming from all over the world.
- Maramures - part of the Hungarian and Austro-Hungarian Empire until WW1
- Wallachia - an independent country in the Ottoman Empire's sphere of influence
- Bukovina - part of the medieval state of Moldova and, later, of the Austro-Hungarian Empire until WW1
- Moldova - an independent country in the Ottoman Empire's sphere of influence
- Dobrogea (region in the S-E Romania, delimited by the Danube River and the Black Sea) - province of the Ottoman Empire until the Independence War in 1877
- Banat - part of the Hungarian and Austro-Hungarian Empire until WW1.
- Oltenia - part of the medieval state of Wallachia
- Crisana - part of the Hungarian and Austro-Hungarian Empire until WW1
I could write a thesis on every one of those regions, focusing only on the differences between them, even though Romania is quite a homogeneous country in terms of the language and traditions.