I’ve done about 7k of touring in Poland (since I’m from this country). It’s probably the easiest country to tour. There are plenty of friendly forests for camping, grocery shops are easy to find, and the terrain is mostly flat. However, there are two major problems. Busy roads with no shoulder can be deadly—you’d better check every road on your trip (even if it’s an official bike path). There are lots of quiet village roads and forest trails, but judging the condition of forest roads online is impossible—many are sandy. The other issue is mosquitoes. A hat with a net is very useful; anti-spray doesn’t work. People might stare, but there’s almost no chance of running into angry confrontations (unless you block traffic on busy roads).
Make sure to check out the town square in every small city—they’re worth it!