1. AMD is not going out of business, despite the hyperbolic and sensationalistic articles on the net predicting doom. They do have issues with their CPU's not being as fast as Intel's top-of-the-line, but their upper-mid range CPU's do quite well. Their graphics division, previously ATI, is also holding its own against Nvidia. Keep in mind that AMD doesn't actually make the graphics card, MSI does, as does Asus, XFX, and other manufacturers.
2. You don't need two GPU's for this kind of work, unless the rendering program can utilize it. If it can, you would need two high-end GPU's. To use more than one card, the program will also need to use be optimized for AMD's Crossfire or Nvidia's SLI. I don't think Maya is optimized for this. But the cost and hassle of using multiple GPU's may make it troublesome. Also, keep in mind that processing an image for CAD versus a game is different. In CAD, the aim is for precision over speed, in games it is for speed at the cost of precision. This is why AMD and Nvidia put out professional cards for those who cannot make do with consumer cards. These workstation cards are hugely expensive versions of consumer parts with altered firmware.
3. This is a tricky one. You mention 3D content creation and RAM. This type of content is really the only reason, aside from scientific processing and rendering, that can really eat up all the RAM you can throw at it. Games almost never need more than 8GB, but CAD and 3D rendering do. To get the most benefit, you must use a 64-bit OS. Also, Windows 8 does have better memory management over Windows 7. This is one of the things Microsoft changed, this
article explains some of it.