ICPI has classes in some parts of the country. They can offer some great information as well. You'll find some debates here between me and Rex Mann (who is an ICPI instructor) about what the 'right' way is to do something. Ultimately, if the resulting work is in great shape after years of use, then "you done good."
My first bit of advice would be to find a few guinea pigs - friends or relatives willing to get some work done for the cost of the materials. Install some in your own yard, too. You hit on an important point here - installing is one thing, designing is another. You'll need some practice knowing what is feasible and what isn't before you get too crazy with your designs. Know how wide a walkway ought to be (did you know most residential concrete sidewalks are 5' wide?), how much space you need between the steps leading to patio doors and a patio set, know how big the typical patio set is, and how much room you need around it for your client and their guests to navigate it comfortably...
You can do most of these things in your own backyard, with a little trial and error.
As for installation - run some searches here, and let us know where there are gaps in the info that need filling in. Too much to cover to just start rattling off stuff.
And if I ever put together my manual, I'll send over the part about pavers.
Oh - check with your local suppliers - they often will have retaining wall classes or paver classes in the winter.