I'm not sure I have specific answers, but I'm pretty sure that you can change the start picture- probably through the control panel, and the personalization options, same as changing your background.
As for the start menu itself, it's a lot easier to navigate if you know that you can just start typing the program you're looking for, and it'll auto-search for you. If you don't want to use it, for the most part you can stick to the desktop, as long as you pin your most-used programs to the taskbar, and have anything that doesn't fit there on your desktop. Then you'll only need to touch the start menu when you're looking for something random on your computer.
Also, that little windows button on the bottom left of your keyboard is your best friend when it comes to the start menu- it toggles back and forth from the start menu to the current program you have open.
Source: daughter of a Microsoft employee, have been playing around with Windows 8 for months at my dad's office. I was super confused about it at first too, but when you figure out the little keyboard tricks, it makes it so much easier.
EDIT: Also, from the Start menu, if you click on the Profile name in the upper right, it'll give you an option to change your profile picture. From the menu it takes you to, you can scroll through all of the personalization options. Probably the easiest way to get there.