Six days is just enough to do the itinerary I suggested, but it depends on how the transport works out. I would want at least two days and two nights in Dubrovnik, and a full day and night in Zagreb. Then you could drop in as many stop-offs as you like along the coast, but remember not to pack the itinerary to tight. Maybe Split and one island?

I'm not sure how you would get from Orhid. By road, you're looking at going through Kosovo or Albania, Montenegro, and possibly BiH. Lots of border crossings, possibly some hassle, and either several changes of bus or a hell of a car paperwork headache. It's not a simple journey.

There's allegedly an airport (OHD) with infrequent service to Belgrade and Ljubljana, amongst others. You could fly to Ljubljana (my favourite city on earth) and take the the train to Rijeka on the coast, then begin your slow journey down the Dalmatian coast from there. Once you reach Dubrovnilk, you could fly either to Zagreb, or to your next stopping point in Europe. But you would want a couple of days in Ljubljana, and then your 6-day timeslot begins to look a bit small.

If the flights from OHD are no-go, then it's a few hours by road to Skopje, where there's a bit more choice.

I guess what I'm saying, is that the far south of Croatia, where Dubrovnik is, is a bit of a dead-end as far as easy, reliable, comfortable travel goes. From there on you're looking at long bus journeys and complex border crossings. While that makes for a memorable trip, it's perhaps best saved for when you have a bit more time! In fact, if you don't want to backtrack by ferry or plane towards Zagreb, the best escape might be on the overnight ferry to Bari in Italy!

Remember, also, that with cheap flights and slow land travel, it might make sense (financially and timewise) to fly via London or Vienna etc to get from Skopje to Dubrovnik.