The rails are installed at the top of the cabinets only. There's a tutorial on the suspension rail in Tutorials:
Suspension Rail Installation.
You shouldn't need additional blocking to support the rail. If you can get at least 2 (although I think any rational person would recommend as many as you can get) screws into studs along the length of the rail, you have sufficient support. The rails have multiple attachment points, so there shouldn't be any issue with not being able to hit a stud.
As for how much rail you need - you need to calculate that based on the length of your walls. The rails are 80" or so...figure out how many you need based on length, taking into account any that must be cut - you can reuse leftovers elsewhere, providing again that you can get at least 2 screws in. Calculate how much you need/80" and order that many rails. Since it's a component system, everything you need is ordered separately. You'll do the same type of calculation to determine the amount of toekick you need.
Hope that helps!
Susan