There are quite a few Singapore guys here in Pentax forum (including me)..
Generally, if you are looking at the new DFA lenses, US will be cheaper than in Singapore. Any lenses you have in mind? Maybe we can advise you on the price easier..
On the must shoot locations, I supposed most tourists in Singapore will be shooting the Marina Bay Sands, Garden by the Bay, Chinatown
The pentax community do organize gatherings once awhile so maybe you can join in one if the chance arise
Shooting the Central Business District (CBD) from Marina Bay Sands
Marina Bay Sands
Garden by the Bay
Buddha Tooth Relic Temple at Chinatown (note: the temple only light up at night on special occasions.)