I just returned from a weekend in Bombay. Saying that, 48 hours was enough to see everything I wanted to see. Having 4-5 days I think you will have enough time to explore things outside Bombay as well.

I also tried Bombay nightlife, which was very very hot and fun. Highly recommended. Bombay is a very mixed city, ugly and beautiful at the same time. It's very colonial. Went for lunch at the Taj Palace Hotel, which was nice. Stayed at a hotel called Chateau Windsor, close to Marine Drive. Not recommended. It was too basic for me, and not up to the positive reviews I had read on Tripadvisor.

I did not find the traffic in Bombay to be a big problem, I think Delhi is much worse!! I would recommend InterContinental Marine Drive, visited the restaurant and the bar on Saturday night, and it was very nice, good food and great service. A great location on the Queen's Necklace, a mere 10 minute walk to Victoria Terminus and 15 minute walk to Gateway of India. I think this hotel goes for 320 USD per night. I found Bombay to be a pleasant city to stroll around in...I did not encounter any problem of any kind.

Have a nice trip and enjoy Bombay