OK, time to give a controversial answer!
Purchase a Full Frame pro-level camera of high standard straight from the get-go! Then also purchase high-end glass lenses!
I recommend a Full Frame DSLR. A full frame produces far better results at higher ISO's and will also produce more usable image information.
Nikon: D700 is very affordable and produces excelled files with a wonderful innovation called D-Lighting (be sure to look that one up). As Jasin Boland would say "it sees better in the dark than a cat full of carrots"
Canon: 5D is another full frame camera with even more megapixels, but it doesn't quite have the dynamic range or sensitivity of the D700.
The best lenses to purchase are:
1. 50mm f/1.8
2. 85mm f/1.4 (The best portrait lens in the world and very well priced if you get the "D" version that has been out for more than 20 years)
3. 70-200mm f/2.8 (with vibration reduction)
4. A nice f/2.8 wide angle lens.
Oh yeah, don't forget to make sure your lenses are manufactured with great glass. Most amateurs and enthusiasts have never purchased the top glass so don't realise that it's the lens that captures the image and the camera that processes it. Without good glass it doesn't matter how good the body is, the results will suffer.
Part of the learning process involves inspiration. If the results you are getting from inferior equipment are frustrating you then the chances of being inspired are reduced. Inspiration increases drive to learn more and quickens the journey to being a successful artist.
I often read blogs and answers from people ranting on about starting small and building up, but I believe that if you want to learn how to produce professional results then you need professional equipment.
Sure, some will crucify me here and say, "What amateur can afford all the gear?" but I say this, "If you're serious about your chosen profession then get serious about the tools you use and find a way to acquire them. Buying entry level gear and then moving to the pro-level equipment will end up costing you far more in the long run, so buying the best upfront will actually save you money!"
I hope some of what I've said helps to some degree. Good luck in your endeavours and happy shooting!