For transportation between the Baltic capitals, I would definitely recommend the busses. They are comfortable, the schedules are packed, and dirt cheap.

A month ago I took luxexpress (www.luxexpress.eu) between Tallinn and Riga, and Riga and Vilnius. The drive is 4 hours, but the busses have a "business lounge", a separated compartment at the end of the bus, where 4 people sitting share a table, there's a 220V power socket and WiFi coverage. There, you also get a bottle of water and a bag of nuts to munch on. Both business and "economy" parts of the bus can use a coffee machine onboard free of charge. The rides in the business lounge cost me 22 and 17 euros, respectively. As I said... for 4 hours' drive each. Amazing Tickets can be purchased online, you just print out your boarding pass and bring it onboard.

They also have a bus route from Warsaw, but that's just too long a journey to endure on a bus... If I were you, I would fly into VNO from WAW, then take the bus up north... or maybe fly into TLL initially, then go down south to Vilnius, from VNO to WAW by train, and then to KRK...