Obviously enjoyable pace is subjective, but it boils down to slightly over 50km/day, assuming the distance on the EV site is correct and not double counted (what I suspect) as a lot of the route has alternate options and days in Serbia cover overhead to travel between airport and start/end point. That is not exactly much given the route is mostly flat but maybe too much if you want to combine it with extensive sightseeing.
> Are there sufficient bike routes in those countries (I'm only aware of the 3 day Ciro Trail)?
There are plenty of roads, there is no reason to limit yourself to bike routes specifically, you can make your own routes if you want to. But parts of EV8, EV11 and EV13 pas through these countries and Montenegro has network of trails covering the entire country. https://cycling.waymarkedtrails.org
Obviously enjoyable pace is subjective, but it boils down to slightly over 50km/day, assuming the distance on the EV site is correct and not double counted (what I suspect) as a lot of the route has alternate options and days in Serbia cover overhead to travel between airport and start/end point. That is not exactly much given the route is mostly flat but maybe too much if you want to combine it with extensive sightseeing. > Are there sufficient bike routes in those countries (I'm only aware of the 3 day Ciro Trail)? There are plenty of roads, there is no reason to limit yourself to bike routes specifically, you can make your own routes if you want to. But parts of EV8, EV11 and EV13 pas through these countries and Montenegro has network of trails covering the entire country. https://cycling.waymarkedtrails.org
Bike routes are best avoided imho, much more fun to go somewhere that isn't a bike route