Yep there's a heap to do in Sydney, so it really depends what kind of thing you like.
If you're a first-time visitor I'd recommend seeing the standard tourist things: go to Circular Quay, check out the Opera House (and have a beer next to it at the Opera Bar), if you're keen you can climb the Harbour Bridge (but you have to go on a tour group and it is very $$$). Check out some beaches too - Bondi is the most famous but I think overrated. There are many better ones, but be warned it's too cold for swimming in May unless you're very brave (water temp will be around 18-19C). If you have a whole day spare you can hire a car and drive to the Blue Mountains (about 2 hrs west of the city), but if you're from a hilly part of the world you will laugh at what we call 'mountains'!
Food-wise, you can find anything here. There is a LOT of Asian food (all varieties) if you're into that, as well as European, Nth/Sth American, etc.
For drinking there are upmarket bars in the CBD (especially nearthe Harbour), and more funky/chilled places through Kings Cross, Newtown, and Surry Hills (all a short ride from the CBD). Tell me what kind of bars/eateries you like and I'll try to give you some suggestions. Tipping in bars is not expected in Australia - you can if you like, but no-one will care if you don't. The base-wage for waiters/barmen is OK here, so they don't rely on tips.
In terms of clothing and fashion, I'm not the right person to ask. The CBD has the usual array of shops that are in any big city, and I doubt you would find any thing here that you can't find overseas. For more underground fashions or second hand/vintage, try Oxford Street (Darlinghurst) or King Street (Newtown). There is nowhere selling IH!!!!
This is all fairly general, but if you let me know what kind of thing you're into I may be able to help more.
One final thing - a lot of people overseas have the idea that Sydney is warm/hot all year round. Not true! In May we are heading towards winter, so the days are fairly short and cool (occasional quite cold). If you stay near the city you can expect the nights to be around 10-12C, and days around 18-20C, so you will need at least one mid-weight jacket.
Hope this helps!!
RnR