Yes there are install guides about
Firstly make certain your CFS3 stock is a clean install as they say having been upated to v 3.1a from the Microsoft offical website for CFS3 only.
The add-ons use the stock files as a "foundation", and if you modify CFS3 files prior to installing the add-ons, you could corrupt the auto-installers.
So only install the Microsoft CFS3 updates before you install the add-ons.
Also, depending on the OS you are using, and of course your Video Card there are some critical things to know about, especially for multiplayer.
Definitely look into reading the CFS3 Tweak Guides online for that too.
In one add-on install you will likely need to change the folder path of the installers if you are using a Dual or Quad Core processor, including also some editing of a few entries in a .bat file because it was done back in the days of the dinosaurs or something, lol just kidding, but it is required as stated above.
There's alot more to cover but it's all case and user specific beyond that except to say that ETO 1.3 is being released soon so keeping a stock/3.1a version of CFS3 ready to install it is a good idea and if you have anything you get stumped on imparticularly I'll try to let you know how I did it here.
It's 5 o'clock somewhere.