Firstly OP... do it! the chance might not appear again!
Perth is a nice place, most people appear to be living the dream. Friends of mine who live over there say it is great an when I visited it was indeed really nice. However for me it felt busy and rushed and the only fights I've seen on a night out in Australia have been in Perth... maybe it's the places my mates took me.
Anyway I moved to Adelaide over 18 months ago. If I'm honest the place picked us due to work but I'm glad as I bloody love it here! It's busy enough for me yet still retains the small town charms like quite parks streets at the weekend. Biking is a 15 minute drive or if like Zokes is stright from the front door. Lots of trails and at over 700m the hills are a reason size. I'm also 5 minutes by car to the beach which is fantastic for evening walks. Also the beaches in Adelaide are pretty empty and that's due to not being overly populated.
Making friends can be hard, you have to put yourself out there. Joining sports clubs can help break the ice and does pay off.
You'll not know if Perth is right for you unless you give it ago... stay a few years get your PR then you're laughing. (note we got PR from the outset so haven't had to worry about visas etc which could have made it easier for us to settle in)
Driving wise.... well the UK is that great either.... I do hate the undertaking bit and driving everywhere at 60kph (37.5mph) can be dull so no wonder idiots think it's ok to eat cereal whilst driving let alone be on the phone texting etc
I'm sure lots of folk on here will be willing to help you out regardless which city you live in.