Poland trip - need suggestions!

I am a car guy, but I would ditch the car and do this by train. Since your vacation starts in Krakow and ends in Katowice I would do:
Krakow (3) - Warsaw (2) - Torun (1) - Poznan (1) - Wroclaw (2) - Katowice (in on the 27th to get ready). A fast trip but 10 is a quick trip. Trains will get you there faster and probably without too much hassle. By the way I have been to every one of these and like Poland their beautiful.

I agree, use trains. They are inexpensive and so efficient! We used trains for our roughly 3 week trip to Poland. There are a lot of previous posts on Poland, this is where I got help planning my trip. In 10 days, if it were me, I'd do Krakow, Wroclaw, possibly Poznan and Katowice. If you like mountains and the outdoors, you could substitute Zakopane for Poznan.

What are your interests? City life, nature, history, culture, partying? Assuming you know about Auschwitz and the salt mines.

Zakopane, a long-time mountain resort area is a pretty popular. Czestochowa is a major religious shrine and cultural hub for Poles. Any chance you could fly into Warsaw and out of Krakow?

You can rent a car for a day and from Krakow visit the Trail of the Eagle's Nest Castles, a string of 25 medieval castles and fortresses, built by King Casimir the Great of Poland in the 14th century, as a bulwark against the encroaching Kingdom of Bohemia. The castles are located in a protected area called the Polish Jurassic Highlands, a hilly landscape of Jurassic limestone cliffs and valleys, dotted with many charming villages and dense forests. This is a daytrip not many foreigners know about but is probably the best daytrip from Krakow if you want to see castles.

I visited them driving with a rental car back in 2019, here is my trip report - https://community.ricksteves.com/travel-forum/trip-reports/new-daytrip-from-krakow-eagle-s-nest-castle-trail

Thanks for all the replies, they helped a lot!

Since you'll be in Katowice for this event, you can go in a different direction other than that to Krakow.

Katowice was the former province capital of Upper Silesia, take the train to Pzczyna, a town also located in the same province, to visit its famous historical castle, Pszczyna Zamek / Schloss Pless. Logistically, much easier going from Katowice than from Krakow.

I would absolutely not miss Wrocław, it easily became my favorite city in Poland. I would also recommend heading to Zakopane. The town itself is meh but it’s a gateway to the Tatra Mountains, such a beautiful part of Poland. Torun is a cute medieval city that doesn’t need more than a day but is absolutely worth the visit.