Actually Tony there are no definitive answers to a lot of your questions as in most cases "it depends".
So:
1) The best computer you can afford that is qualified to run Maya. Go to Autodesk's website to find a list of tested and qualified systems. You certainly do NOT need 16Gb of RAM to run Maya and will likely only need that much for extremely heavy scenes or simulations. Maya will run fine with as little as 2Gb of RAM, though I wouldn't recommend it. You need more memory as your scenes get heavier and you need to load more file textures.
2) Every studio has its own pipeline, but in most cases at those big studios they use third party 3D paint programs extensively. Mari is the next big thing in this field.
3-5) It depends. Resolution is determined by how the pixels from your image file will correspond to the number of pixels they will occupy in your renders, with the optimal being a 1:1 ratio. In practice, you usually have to make an educated guess and just make sure they are big enough so they don't pixellate in your renders. File format doesn't really matter as long as it's supported by all the apps you use, though you're normally better off avoiding JPG and using something that is relatively uncompressed like TIF or TGA.
6) It depends. Procedural textures have their pros and cons. Some pros include resolution independence, less need for good UVs (in the case of 3D textures). Cons include difficulty in art directing them, noisy in renders. Every situation is different. In many case even when procedurals are used it's best to bake them out to file textures for final renders.
7) Keep your file textures as small as you can, reuse them in scenes as much as you can. The objective is to use the smallest amount of memory/RAM you can.
8) Compositing is part of any decent 3D project, but with render layers and passes in Maya it's often possible output all the elements from one scene. It depends. More complex pipelines at larger places may work differently.
9) You can certainly model most things in Maya if you want to. There are other programs out there, like Z-Brush, which may make it easier to do certain types of modeling. Maya can do most things but there are other apps which specialize in this or that. There's often multiple ways to get to the same result in the CG world.
10) It depends what you want to do and your experience level. If you are a complete newbie, maybe a community college to get your feet wet. If can get a copy of the software, do so and start doing tutorials (tons on places like YouTube). Expensive college programs will not make you job ready, despite their claims, and the only way to really learn 3D animation is by yourself and with many, many hours of practice. Get an internship or join an online volunteer project to get some production experience.
11) It depends. With a "Hero" tree that will be seen up close it's likely to be a combination of model and texture. Objects farther away will be done mostly with textures because it's cheaper/faster for the computer to render.
12) Lots of ways to approach a problem like that, such as using a procedural texture as a displacement map (like a fractal). There are also other apps (such as Bryce) which specialize in natural environment type stuff.
13) It depends. If you really needed to do this you would need to make the projections "stick", such as with a texture reference object.
14) You normally only use projections when direct mapping doesn't work for some reason or there is some advantage to projecting.
15) Not normally. You don't need to separate geometry to have separate UV maps. Complex topic though.
16) Again, it depends. Some things are just more easily modeled with NURBS so they are still around. Everything ends up as polys in the renderer though.
17) Each light type has its own uses. Get a book like Jeremy Birn's "Digital Lighting and Rendering" to learn about them.
18) I haven't used it but again it likely "depends". Sometimes those potted systems in Maya are all you need, other times you need to use a more adaptable approach.
HTH!