There is one thing to chip in that none of us have mentioned (edit: at least when I started writing this ...
A camera is a handheld tool just like a plane, a chisel, a saw or a screwdriver.
For your very first camera, you don't really know what you like, but after you've had a camera in your hands for a few dozen hours you begin to get an idea. At that point, the easiest thing may be to go to a photography show where you can mooch around the stands and just pick up and handle the main models from the main brands.
When my own camera was first launched, it took a few months before I was able to see and feel one in the flesh. Before that it was just "that looks neat and the specs are "wow!, but ouch, so pricey". Once I'd handled it, I knew it fit me and I had something to save towards.
Cars tend to be the same. Sit in it, drive it, and you know it's the one for you.
Sony, Nikon, Canon, Fuji - they have their own style and ergonomics. They also have niches where they have advantages over each other. For instance, Fuji had some great success with small, quality cameras well suited to candid urban photographs. Sony as Paul says are making very high technology cameras.
It is not necessarily a bad thing to realise that a particular brand and even an advanced camera is the thing you aspire to, then to buy an older more affordable model from that brand as a learning tool. As others have said, committing to a lens mount is the single biggest deal because they aren't interchangeable. The best investment is in glass. A lens can last 10 years before a newer version is released and easily 20 years in use. Cameras are superceded on about a 3 year cycle because the tech in them evolves faster and pro may swap every 3 years or every 2nd update depending if the changes give them better images and lead to more work / sales.
So, take a look at when the next camera shows or open days are around your way and consider going. Go with a clear agenda - not to buy but to get a feel for the brands and an idea of where to aspire, and use this to shop for an older used model.