Should I attempt a long trip?
180 km is a long way for someone who only normally does 20-30km (to quote @PeterH in chat).

To my way of thinking, you could do it, with some pre-conditions


Do some longer rides, where you ride 30km to somewhere, have lunch, and ride back.
Ride on some of the potential routes, to understand the traffic situation.
Plan ahead, so that you do it over two or more days.


I would check out where other people ride. For example


Strava activities near Bucharest
Strava activities near Focșani. A lot of these go into the mountains, but you may find some that go where you want.


And use Google Street View for reconnaissance.

A few related questions and answers


What is the necessary equipment on longer bike rides?
Help for a 169 mile bike ride
Training involved to ride 175 miles (281 km) in a day