The Axe-Fx III can be as simple or complex as you want it to be. As has been alluded to, keep things simple. It's easy to get overwhelmed and overthink things with all of the options available. Look at the Axe as a virtual shop full of all of the amps and effects. Choose an amp you're familiar with, select a cab that's typical for the amp and tweak away as you would on a physical amp. Add your effects and continue tweaking them until you arrive at your desired tone.
You may go as far as taking a piece of paper and making a list or diagram of the rig you want to build and the configuration you want. Then build your rig, sticking to the blueprint you decide on. I would
highly recommend using Axe-Edit III when starting out. While working on the unit itself has improved greatly due to the new user interface, Axe-Edit is much more visual and easy to navigate in my experience.
I would also recommend downloading the manual to a computer or tablet and use the search function to quickly find the subject you want within the PDF. Also bookmark the Axe-Fx Wiki,
http://wiki.fractalaudio.com/axefx2/index.php?title=Category:Axe-Fx3 . The answers to most of the questions you'll have will be found there.
As you've discovered, the forum is a great resource as well. Don't be afraid to ask questions but don't take any replies personally if the question is very basic and/or found in the manual. There are plenty of guys here with the experience and expertise to help you along the way with more than "Read The Manual" replies but you will inevitably get them. One thing that does help is learning the terminology and what they mean, i.e blocks, grid, scenes, presets, channels etc.... These terms and definitions are easily found in the Wiki. There is a learning curve but if you'll take a few days at the very beginning to become familiar with the basics, it will make things a lot easier.
As far as gear; it all depends upon your needs. If you're used to a large pedalboard, the FC-12 may be the right choice for you. I used a moderate pedalboard and the FC-6 has more than met my needs. An expression pedal would be a good idea and is much more valuable than a volume pedal in my experience. A volume block can be placed anywhere in the chain and different places per preset. If you already have a volume pedal, you can use a Y-cable (dual 1/4" TS to single 1/4" TRS) to use as an expression pedal. The pot value may influence the response though.
Finally; relax, be patient and have fun. Everyone of us started exactly where you are at some point in our Fractal journey and have made it through the process with great success. Good luck and I doubt you'll regret the decision to go with the Axe-Fx III.