Hi,
I'm also originally from Manchester and have recently moved up to Queensland after a year in Melbourne. Melbourne is a brilliant city with so much to do both in Melbourne itself and in the surrounding areas. I loved my time there, but I have to admit it was the weather that made us want to move. It is considerably better than Manchester, you will certainly spend more time outdoors there, but like so many have said, the whole '4 seasons in one day' thing can be true. It can be pretty unpredictable and there's only a small part of the year that fits that Australian dream that so many of us come out here with. Temperatures in winter get higher than back home, and don't go as low, (I do not miss scraping my car every morning!) but it is still cold in winter, and I mean coats & scarves cold, not just 'put a jumper on' cold!
We are very much beach people, my partner is a keen surfer and we love to spend our weekends by the ocean. Yes you might have to travel a bit if you plan on living in central Brisbane, but the same is true of Melbourne, the nice beaches are at least an hours drive from Melbourne. We live about 30 mins north of Brisbane and we love it because there are beaches 10-15 mins from us, if we want to go a bit further we go up to the Sunshine coast or even down to gold coast or Byron, there are so many options here for the weekends. That said, like others have said, if you will be working outside you'd have to consider the implications of living in a state like Queensland as apparently the summers can get very uncomfortable. I hope you figure out the best option for you, as personally it's the best thing I ever did and I love my lifestyle here and can't wait to raise my family here.