You can exchange on street but I don't advise it for Luanda novices and/or if you don't speak Portuguese.
Kinguila Hoje - Noticias, Dolar e Euro paralelo em Angola - gives you rates. Best to get a fixer from your host's company to change your money or you could ask your hotel's reception to do it but agree in advance the rate you expect.
If you change at an official exchange booth you will get a far worse rate. It is safer though.
The Ilha is the place to go at night. I quite like Club Náutico for early evening drinks as you can see the yachts and the city illuminating as night falls. It is also quite cheap and OK for dinner. Cafe del Mar is also nice for lunch and afternoon drinks. Lookal is nice to splurge on a seafood supper.