I might sound like a know all, but---- I have been married to a Goan chap for 20 yrs and we spend our holidays there & have a small house[ in Ribandar in Old Goa not near the tourist area]
50s or 20s are easily changed, euros forget it half of them havent even heard of them.
Travellers cheques can be changed at your hotel but you will get a bad rate, all the banks [ as far as I know] are situated around the capital Panjim area and its approx 40 mins from the tourist area i.e. Calangut, Candolim & Baga
Ask any taxi driver to take you to local money exch if you dont spot one by yourself..
Change about �20 into rupees at Gatwick, they have to tell you by law its illegal and then they change small amounts for you, this will help with small tips etc dont forget they earn peanuts at the hotels and 100 rupees is a big tip for them.
In Calangut there is an open air, all night, night club called Titos, the most popular place to eat is called Britos, very popular with the Brits but pricey by Goan standards, there are so many bars[ some with satellite tv] and places to eat, try along the beach and just visit a different one each time until you feel at home, the Goans are very friendly but most bar owners/ waiters are not Goan at all they drift in for the holiday season.
Whatever u do do not go all inclusive, who wants to eat the same meals for 14 days ? and booze is cheap unless you visit the Taj or Marriot hotels.
If in Candolim [ next to Calangut] -- walk along the beach in opposite direction to Calangut/Baga and go to the very last beach restaurant its great, clean kitchen,good food, cheap and they are so friendly and will cook you anything you want but not on the menu, also get you a taxi back save all the walk, this place is not visable from the road.
Dont forget to visit the spice fields, forget the crocodile farms too many mosquitos.
Happy to answer any other questions if I can.