I felt the same way when I left Toronto to return to Johannesburg. I lay awake at night thinking about all the reasons not to go. Why would I leave my comfortable life? Why would I turn everything upside down? Why would I distance myself from my friends and family? Why would I go through all the administrative and logistical trouble to experience something new? Why would I risk my safety and security? Why would I commit to something that wasn't fully locked down and predictable?
The answer is this: because you will become someone new. You will allow yourself to grow and change and adapt and learn. You will make new friends and expand your world in immeasurable ways. Your diversity of life- and work-experience will benefit your future employment, relationships, and outlook. Because you are young now, and there is no better time in your life to try new challenges. When you get old and settled down into a predictable beige life, with your beige computer, and your beige wardrobe, and your beige walls, and your beige mortgage and beige responsibilities, it will become harder and harder to do things for the sake of doing them. The opportunity is in front of you, the door is open, all lights are green; all you have to do is proceed forward. I say go for it.
Anyways, Toronto is a great city. I currently live here, after having lived in Johannesburg. Also New York, Nairobi, and have been many times to London, Paris, Brussels, Amsterdam, Berlin, Barcelona, Geneva, Sydney, etc.
Toronto's standard of living is by far one of the more even keeled of all the above, for what you pay for. Since you're coming from the UK, you'll find everything here ridiculously cheap and of excellent quality. All my Brit friends travel here with empty suitcases so they can take advantage of the favorable exchange rate with the GBP.
Its one of the most culturally diverse places in the world, and has a "big small town feel to it. This means that you'll get great authentic food choices at amazingly cheap prices with great quality produce. The foodie scene is excellent, and Ontario wines are global award winners. It also means that there are a lot of expats in the city - people who come from other places, and I don't think you'll have a problem making friends.
The downtown city is small enough and safe enough to ride a bike around, walk or take public transportation (streetcar trolleys, buses, and subways). While recent crime has spiked to a remarkable high and received a great deal of media coverage, it is still one of the safest cities in the world according to population.
Gay life is amazingly prevalent and accepted without much concern. While there is a gay village, gay events and people are also integrated and spread througout the city's various neighbourhoods.
One of the charming things about Toronto is that residential neighbourhoods are nestled throughout the metropolitan area, so you can be driving on a large 4 lane highstreet, take one turn and be on a tree-lined residential street with Victorian gable houses from the early 20th century.
Last winter, the temperatures average from -1*C to -8*C (wind chills can make it feel colder and drier than the temperature guage reads). Summer temperatures hover between 25*C to 35*C (but high humidity can make it feel hotter than the thermometer reads).
Toronto is about a 1.5-2hour drive to Niagara Falls, and a 6hour drive to Montreal (45min flight), and an 8hr drive (1h15min flight) to New York City.
For rentals, check http://www.kijiji.ca