i cycled through montenegro/kosovo/macedonia recently, so not quite the same but i’d expect similar conditions – roads were mostly fine with a few exceptions on smaller routes, one part had roadworks meaning no surface for a couple miles etc.. but not bad for the most part.
i found trucks to be reasonable, most beep (to let you know they’re passing – that might be fairly close at times but i didn’t feel at risk). Vehicles will overtake each other coming towards you which is disconcerting, and will pull out from side roads as if they haven’t seen you (but seemed to do that with any traffic really – if they can get a nose in, they will go) so anticipate both and you’re fine.
100 a day should mean you have plenty time for either bike though i’d go for the audax personally, if both have skinnies then it doesn’t make any difference anyway.