Hi
Thought poland was great from my brief forays into it. Ia berlin and Munich. Both are a three day (for me I travel slowly). Tatras can't comment on as haven't ridden in but looks like you have plenty of time. Be interested to see what you think. Would imagine temperatures still pretty low if you go early May. Wrap up! If you use tom tom gps and tyre route plan software I'm sure I have routes saved to get you to poland if you like.
Enjoy the trip sounds great.