The Novotel is pretty good and as you say good value. It is in Tung Chung (東涌) which is on Lantau near the airport (decent outlet shopping centre attached too). The good news is the MRT stops in the basement of the shopping centre so getting around won't really be an issue for you.

The Tung Chung line takes maybe 25-30mins to get to HK Station which gets you to the CBD. You can also walk across from there to Central Station or catch the Star Ferry if you want to get too TST or Mongkok etc.

I wouldn't worry about walking on your own at night, HK is pretty safe and I've never felt in any danger at any time. You tend to find that there's always people around.

What type of bars/clubs are you looking for? Can give you some recommendations. In general a lot of people go to Lan Kwai Fong (蘭桂坊 or LKF) as there are plenty or bars, clubs and restaurants in the area (and it's easy to get too)