I'll tell you something hopfully usefull about trains in Poland.
We have Intercity Trains (IC) with seat reservation, which are the fastest, would stop only on major hubs and are with best blessed with best quality customer service, where you'd have restaurant car and some trains would even have an internet access. Food is actually good there but there's not much to choose. Anyway you'd be better off having your meals somewhere else but it would be still nice to have a break in reastaurant car on longer routes especially. There's also someone selling snacks and drinks, newspappers on IC trains. No smoking anywhere.
Another type are the Express Trains (EX) with seat reservation as well - they differ from IC that they don't have restaurant car but usually would have a snack car with drinks. EXs would also tend to have more stops then EC and would be somewhat slower then EC.
Then we have the POSPIESZNY P (fast) with no seat reservation -those trains are most popular, usually you'd have many connections to choose from, trains do stop in biger and some smaller towns but do not in very small towns
OSOBOWY O (regular) Osobowy stops on every train station along, often every 15 minnutes or so. Good for shorter trips.
Here are my sugestions for your route
Gdansk - Torun - take P - 36PLN 2nd class or 54 1st class, TIME less then 3 hrs
Torun - Poznan - take P TIME 2.30 similar price
Poznan - Warsaw take IC - 90 PLN 2nd, 125 1st, TIME 3 hrs
Warsaw - Wroclaw take IC - 96 PLN or 131 PLN , TIME 5 hrs
Wroclaw - Krakow take IC - 84 PLN or 114 PLN, Time 4 hrs
Krakow - Zakopane take bus, about 2 hrs
and finally at the end of the adventure
Krakow - Katowice take P - 20 PLN 30 PLN, less then 2hrs
Last year we had summer promotion package from PKP where you could take 4 trips on Ex or IC trains anywhere for the price of PLN 150. Two trips on 1st class and two 2nd class. It was called VOJAGER package and is likely to be offered for thiscoming summer. With that package you'd still have to pay for seat reservation on each route (about 25 PLN for EX or 50 IC) but it's overall great value.
Also from Friday 18.00 PM to Monday 6.oo AM for the price of 60 PLN 1st class or 80 PLN 2nd class you could travel all POSPIESZNY and OSOBOWY trains all over Poland, wherever you want.
The ticket's called TURYSTYCZNY and is issued with your name on it. You'd have to show it, when asked with some picture ID. Your name's on it so you wouldn't give it or sell to someone when still valid on weekend.