We guess you are going next year, or some time after that?
Is it possible to get to Croatia and back comfortably in two weeks? Yes. Can YOU do it, comfortably at that time, in that period? Only YOU know the answer to that.
What will the weather be like? Who can tell, exactly. I went to Luxembourg (sort of on your way) last week and it was OK, nothing more than occasional drizzle, with temperatures that fluctuated even with a few miles between 17 C and 7 C. Three days earlier, pissing down, uniformly cold(ish) with some D roads flooded. What do YOU think the weather will be like on the way down and in Croatia in early October next year, if you had to guess for a million pounds or your life depended on it? I guess you’d try your best to make as accurate a guess as you could manage.
Practical advice:
1. Get a map
2. Use your imagination
3. Pack spare underpants and a toothbrush