Glad to be of assistance and I expect that you'll get other advice from this forum too, and offers of ride partners closer to the date if you head up here.
Arts are a bit concentrated in Bris, it in the inner city suburbs. Definitely check the Power House at Newfarm not just QPac & the South Bank precinct area. The Valley is great for live music.
We've had a relatively cold winter this year IMO but even then 6 and 7 degrees are the minimum around the city and northside and most days the min is over 10. For those west of the city where it certainly has got down to 1 or 0 on occasion but that isn't typical. The days also warm up pretty quickly will with most days having max in the winter of 20+.
I recon you'll love late March/April/May for temperature and lower humidity, though even March can throw up a warm period. If you are happy to get up a few Ks on the bike there are good rides to do that take in lots of local areas of interest Mt gGllorious, Mt Cootha, Mt Mee, Sunshine and Gold Coasts and hinterland, and if you mix it up with the train and your car you should have a great time.
Having said all of that if there is a festival or arts event that you want to see, come when it is on, we really do have pretty good riding all year, just treat the heat with respect

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ENJOY!
