Oops! That was a lot of questions on many countries. Wonder if anyone can answer. (Very few sailors visit all the places the same year and can compare..
I take the easy part opf your question - favourite places:

Germany
Former DDR. This part was not heavily bombed during the war. And due to lack of money, DDR never replaced the old hoouses. Thus you can find an "old" Germany here. Hint: Spend some time behind Rügen and sail the inner way into Stettiner Haff and Poland.

Poland
Leba and the Sand dunes
Hel is nice

Lithuania
If you can spend two days more. Sail down to Nida in Kuricheas Haff and up again to Klaipeda.

Latvia
Liepaja, Pavilosta on the Baltic coast. Roja near Ruhnu (Runö)

Estonia
Ruhnu (Runö)
Kuressaare town
Kõiguste
Hiiumaa (several harbours)

Finland
Sailing westwards, stop at Kökar

Sweden
Outer skerries in archipelago. Try Rödlöga island in the north. Thge places of the archipelago foundation is recommended. There are thousends of islands. You need good charts. Avoid the Marinas, the small islands are better!

Further south:
Small town Trosa
A ha5rbour on island Öland
Utklippan lighthouse and harbour

If the wind not let you sail South - make a giant leg to Visby at Gotland, and return to Öland (N or S)

Denmark
Christansö, (old fortification island north of Bornholm)

And you plan to see all this in one summer