Rules are often changed, and the rulebooks from 5D's may say different things from GX or original series rulebooks. For instance, 5D's mentions Synchro Monsters, which did not exist in GX or earlier.

Unfortunately, the rulebooks themselves are not available online through legal channels.

This would require an extremely long answer, especially with three different breeds. The first thing you need to do is write or go online to these three registries sites and have them send you their rulebooks. This will describe the classes and what is required to show your horse. While you are waiting for the rulebooks find some shows you can go to so you can see first hand how each breed is shown in-hand. There are certain types of clothes, halters and ways of grooming that will probably not be in the rulebooks. Ask questions and pay close attention to the way the handlers handle their horses. Watch the ones that are winning and observe the ones that don't win. There is so much to know just for this one kind of class.

There is no dungeons and dragons beast. What you have is a vast array of monsters of all types that can be found in the rulebooks. The Monster Manuals are the most common but also check out the Fiend Folio and campaign specific books.

You cannot get Warhammer for free, just like you can't get Tennis for free. The concept and the question don't add up.

You can however get the rulebooks, codices, and miniatures associated with Warhammer for free, if someone gives them to you, or you win them through competitions. The other alternative is to buy them.