Hi Stuey, welcome! This is a first try? It's very good. A nice, natural, unforced writing style and a good storyline so far.
My take on your questions (no doubt others will have something to say too):
Don't compromise your NZ English - it gives additional flavour and interest to your story. In this global community most people can pick up regional variations in English and if they can't they'll ask. They'll be intrigued, not put off your story. I write Brit English and I get readers writing to say how much they like my Britishisms. Only once can I ever remember writing something explanatory for an American audience - I wrote about a CV, and put in a comment that it would be known as a resum? in the US.
The ending of chapter 1 is enough to make the reader want to know what happens next, but not enough to make him squirm and go 'AARRGH - Don't stop there!'. Personally I want to know what happens next between Stephen and David more than I want to know what happens between Stephen and James, but I'll have to be patient. You ARE going to post subsequent chapters here, aren't you?
As for the sex, it's a story about sex, you can hardly leave it out. Whether the amount is appropriate here at AwesomeDude I'll leave for others to comment on. You have to understand we're very sensitive - delicate consititutions, you know. If you could see us, we're all sat around in the drawing room, maiden ladies in twin set and pearls, sipping tea together out of the best Wedgwood, our little fingers pointed outwards, and discussing last Sunday's sermon. So you have to make allowances for us!
I really enjoyed reading this and look forward to more.
Bruin