I wouldn't buy second hand at this point. Get a deal on last year's model instead and save a few hundred quid.
Find a good local bike shop. Not a big chain.
Get fitted properly (it won't be free but will be offset to some extent against cost of bike usually.)
Get one that fits you best.
Don't be sucked in by group set mania, stuff from the quality manufacturers will be similarly equipped but I mean don't be tempted to something that looks better on paper if it fits less well. Its easy to get sucked into the hardware side and in reality its not that important.
For Singapore I'd get a tight gearing set up 53-39 and 11-23 so not a compact which is often standard issue here in UK.