You don't say what kind of a trip you are considering. Length of time, choice of transport, that kind of thing.
If I had 6 weeks, I'd start in Athens, visit Nafplio, take a train to Thessalonika. From there I'd go to either Bulgaria or N Macedonia. I'd then hit Serbia, B-H, and go to Romania. That's trip 1.
On Trip 2, I'd go to Czech R, Slovakia, Poland, Belarus, and Modavia.
In terms of acraven's comment about Romania, I think she's working on old info. We were just there in Oradea and Timosoara, hardly the biggest towns in Romania. We had no problem finding all sorts of decent restaurants. Perhaps in small towns there would be few options, but in any city of any sizable sort, there are plenty of decent restaurants. And they are not cheap. They are a decent value, but you do have to think carefully about food choices. I'm a bit mystified by the warning of insufficient choices of vegetables. We found plenty of options in those Romanian cities we went to. In Serbia, our main complaint was that we had portions that were excessively large.