you have to extract the ini files from the files with the .mix extension. You can do this by going to
http://xccu.sf.net and downloading XCC mixer.
After running it, you'll see that the program is divided into two sections. There's actually a third section hidden between the two sections. Open up the hidden section.
Click through "File" => Found => Red Alert 2 => ra2.mix. In the left section double click on local.mix. Now browse through the left section and find the ini files rules.ini (to start). In the middle frame (the one you revealed), browse to the location where you want to extract the files to. Right click on rules.ini (in the left section) and click "Copy".
You will now find rules.ini in the location where you extracted it to. From there, you can open it up and take a look around.
To apply your changes, just stick rules.ini in the same directory as Red Alert2.
As to your other questions, its possible to put a limit on how many of a single unit can be built, although I don't think you can have an overall limit. Fog of War cannot be added.