You can find all the info you wish rozklad.pkp.pl/bin/query.exe/en - here in English. As to booking before, you can but I doubt it will make any difference as there are always places, especially at that time of day. However for peace of mind just go to the station and book one :)
Katowice Main Railway Station is located in the city center.
Trains from all parts of Poland and other countries arrive at Central Station. There are fourteen trains per day between Warsaw and Katowice and twenty-eight trains per day between Cracow and Katowice during the day; the journey takes 180 minutes.