traveling tips of Poland

[justolive]

i will be traveling to poland later this month, and would like to get some suggestions regarding the following questions.
1. I'll be traveling among cities like warsaw, gdansk, torun, wroclaw and krakow and buy tickets online in advance, but i wonder is reservation really necessary?
2. How come the prices listed on e-ic website and polish railway website are different? I mean, the date, train number, class are all the same, but the prices are not.
3. Is tipping a must? Like waiter in the restaurants, house keeping service in the hotel?
4. I want my meal to be beef-free, no beef at all due to my religion. How to express that in Polish?

thanks