Updated the list of potential lords, we have 26 now and I can easily increase it to 29
Suggested settlements
Towns historical: Krakow, Wroclaw, Poznan.
Gameplay: Krakow Wroclaw Gdansk/Plock. This version is to spread the towns around a bit, making it easier to sell junk.
The first is according to what I know to be the most important cities in Poland at the time within the limit of 3 towns (feel free to correct me)
Castles: (no specific order) Lubusz, Opole, Cieszyn, Sandomierz, Lublin, Drohiczyn, Czersk, Plock, Wloclawek, Sieradz, Kalisz, Gniezno, Dobrzyn, Slupsk, Gdansk, Tczew, Glogow, Santok.
Villages: Tyniec, Sacz, Mogila, Olesnica, Brzeg, Ujscie, Srem, Cedynia, Olesno, Orlowo, Kielce, Lukow, Liw, Sochaczew, Lowicz, Brescz, Ruda, Konin, Trzemieszno, Sierpe, Sczytno, Lebork, Starogard, Zagan, Miedzyrzec.
As KDM noted Leszek and Roman were on good terms in that year and the outbreak of hostilities between them was somewhat sudden. (Up to that point Polish armies usually showed up to help Roman deal with internal opposition.) If/when the Prussian tribes are included than it would probably be historical for them to start hostile.