The main tourist area is in the north in Rodney Bay, plenty of bars and restaurants available. Hotels range from moderately expensive to real bargains (I'm paying $45 a night in mid December for a nice guesthouse in Gros Islet).
The nature sites are near Soufriere, there you will find everything from cheap to God awful expensive hotels. The drive time from the main international airport is 90 minutes to Rodney Bay, 60 to Soufriere.
Staying up in Rodney Bay I would recommend skipping the AI as drinks are cheap and there are a lot of restaurant choices. In the south if you choose a hotel outside of town, you're pretty much stuck with the on site restaurants or taxi/rental car as nothing is really close to anything else.
Near the international airport there is a AI resort, Coconut Bay (I think), but you're not really near anything as far as off site excursions.
International airport down south is UVF
Smaller airport in Castries (20 minutes from Rodney Bay)is SLU
The beaches aren't as nice as in SXM and topless/nudity is against the law.
People are friendly and you will find a lot more of a local/tourist mix at the bars in Rodney Bay than you may be used to in say Simpson Bay/ Orient Beach, probably 50/50.
Weather report will call for rain everyday, it has a rain forest, but typically just a passing shower if anything at all. Very rare to have a full day of rain in the winter months.