Most of your questions have been accurately answered already.
I liked the advice given on style. Yes, you can get away wearing shorts and tank tops but whether that is a good idea is another question.
A lot of the bar scene is around the large international hotels - it all has to do with the liquor licence. A lot of them are of the upscale nature with dress codes enforced, so especially as a guy, you will not risk being sent away.
Ask the hosts if they'd appreciate booze from the duty free. There is a huge duty free at the airport with an ok selection at reasonable prices. The allowance for duty free on arrival is 4 liters. That can be 5 bottles of wine or also 4 liter bottles of vodka.