Balkans trip

I assume you aren't renting a car, because the international drop charge would probably be exorbitant. Have you researched trains (rare) and buses linking your destinations? It's not so easy to get reliable Balkan bus schedules on the Internet, I know, but your itinerary looks very aggressive to me--just a few days for each country. It would not be my choice (I'd spend the entire time in just one of those countries), and if something goes wrong with one transportation leg, the whole thing could come down like a house of cards.

How do you plan to get from Dubrovnik to Athens and from Athens to Sofia?

Does "day tour" mean you plan to take a bus tour, or do you plan to simply get there by public bus? ViaMichelin.com estimates the driving time for your proposed Sofia-Rila-Plovdiv-Sofia loop at over 5-1/2 hours. That's in a private car, with no time allowance for any stops, traffic, etc. Via public bus I doubt this is possible in a day, and a bus tour would give you very little time at both stops. Plovdiv is worth more than a full day by itself; I haven't been to Rila.

ViaMichelin estimates over 7 hours for the round-trip drive from Sofia to Skopje in a private car. A bus (if available) would be much slower. Border-crossing buses are quite rare.

I plan of flying between each country. When I state day tour I plan on using a tour company and have already found these tours online. I typically keep pretty busy days when I travel.