Hey guys, it might be too late for most of you but I saw this topic and thought I'd add my two cents...
I did an exchange at NUS for 2 semesters last year. I stayed off campus at Gillman Heights
condo because I didn't apply for on-campus residences in time. Frankly, you don't need to worry about meeting other exchange students at NUS no matter where you live. The atmosphere among exchange students is about meeting as many people as possible and everyone is extremely open and friendly.
Meeting locals is a bit more difficult as the NUS students are usually pretty busy and not always as open to meeting new people. It's understandable, I'm sure many of us are the same way when we're at our home universities. Nonetheless, I think it would be better to stay in a hall with locals (anything but PGP, Prince George's Park). It's harder to get into but you'll meet locals as well as exchange students.
Singapore is probably one of the best places to study abroad, I'm even looking into graduate school there now ^^
PM me if you've got any other questions, I don't really check this forum anymore unless i'm bored and reminiscing
