Can you get your gas from Sai Kung town centre?
If so, pop in to The Brothers (Hing Dai) Gas shop (on the corner, same row as the HK Jockey Club and Park N Shop) The lady there speaks good English. But you will need to leave a hefty deposit if you are a first time customer ( equivalent to one bottle of gas ~HK$280.)
Again, for the curtains, there are two curtain shops. Go to the one next to the DVD/video shop, they're much more friendlier than the other. But I would measure your window sizes before you go for them to give you a rough estimate. They will ask you to select which material you want, then come round to measure accurately.
Otherwise, you'll have to get a bi-lingual neighbour to call for you.