- Bus: Orange ways
Zakrzówek - is an old quarry just 2km from the castle/center. It's a big wild park where it's possible to camp and swim. There are plum and apple trees growing around, too. 
Pretty budget. You can easily have a meal for even 10PLN (2.50€?). Fun fact - if you turn on TripAdvisor, there are mainly restaurants marked as $ and $$ (Hard Rock Café counts there as well).
To be specific - my favourite restaurant became Gospoda Koko. Local cuisine for very cheap prizes. Pierogi for 10PLN maximum. And you should definitely try some places around Kazimierz as well. Great street food, ice cream, cafés and so on.
Wifi mostly available in cafés, fastfoods and restaurants but you can even find networks in public places.
I was told by a local that you need a permit which takes 2 months to get. But the police didn't seem to care. A good idea would be to play near places where basically no one lives or to avoid shops but while we were playing in one of the most popular streets to busk, some shop keepers even went out to listen.
Money's not bad. 10PLN notes are not rare and we got these at least once a set. We haven't tried to play in night time but I think it's a good idea snce there are not many buskers in the streets and the people are still there. A place that worked the best for us was Floriańska street and the gate at the beginning which has nice acoustics.