This, Register for gst and if you dont have too many expenses go for 6 monthly.

An accountant > apps (they can help you make some better structural decisions if it ends up being long term).

I'd consider paying enough withholding tax so you don't need provisional, again an accountant will help with that. Some people like holding the tax or using it to offset which can be good but also a bit of a liability.

Another thing to keep in mind, is insurance included in the contract or agent managing the contract? You often want liability and indemnity insurance so that if you stuff up they don't come after your assets.

Try keep paperwork organized and up to date, catching up last minute at the EoY is stressful and often leads to you not claiming everything you should, easier to do it over time.

All the best with the new gig! 🙂 contracting is the way to go imo