Im new at this so please go easy:

I'm trying to find a way to use my miles going first class from IAH to SYD. I know Qantas and ANZ are near impossible to get seats on, so thinking SQ. I'm not familiar with their award policy, but being flexible as far as origin (JFK, LAX...), whats the best way for me to get seats? I can transfer points from SPG or AMEX, or pretty much anywhere else (I have plenty). Any suggestions?

NZ isnt too bad on availability as long as can book well in advance (or at last minute) and happy to go in economy. It is business class 1-9 months out that is very hard to get.

What about SQ? Anybody?

SQ is only available as a valid carrier to Australia if you go to Perth. You route via SIN.

For SYD, going via SIN would be 2 awards, not 1.

Sounds like you don't regard UA as having a 1st class, ha ha, but it's a chance for award tickets. If you pay double the miles ("Standard") you are allowed to pick any day, otherwise the normal award (called "Saver") you have to pick a day with availability (several months out, usually, or 1-2 days ahead).

UA's website lets you check award availability, best to register yourself as an "expert" and see all availability.

I fly IAH-SYD four times a year, have found the optimum is to fly Continental to LAX and transfer to UA to SYD. Of course UA's award would include the IAH-DEN-LAX sectors at no extra cost, just be very careful with the connections as if you misconnect you are not going to get F seats on the next day's flight to SYD. Would recommend departing IAH 4pm on UA or 6pm on CO. Coming back through DEN is horrible, always delayed, best use CO.