There are a lot of different ways to do the head - most accurately you want to somehow extend the neck. For most of us that means having the head of the character sit on top of your head. I know maybe people have used a bicycle helmet as a base to put the head on and that's a good start. And foam is your friend - it's light and you can bump into things with out damaging your costume :P
I didn't end up using a bicycle helmet but I had a hole cut out of my character's head that I put my head into - like a hat with straps. I had used insulation foam so just carved the shape right into it. I saw out of the neck just below the jaw and I had great vision in mine. I also had a moving mouth built into mine - I had elastics that held the mouth "shut" and used a strap that was connected to my harness to make it talk.
I have a video that i posted that you can see the head progress if it helps
As for stilts, again lots of ways to do them - most people use the pvp pipe to extend your arms. For my quad I ended up using wooden stilts because I wanted there to get a hinge joint for the "knee" of the front leg so I ended up making something more similar to an arm crutch/brace. I had the wooden post with the hinge and two straps that held my forarm in the costume and a handle for my hand. It works out pretty well for me and i didn't have as much of the stiff front leg look that happens to a lot of the quad costumes.
Make sure that what ever you choose it's the right height for your "hind" legs so there is no strain on your back. Your back will thank you :P
I used a duct tape dummy to plan the pattern of my costume - i put the clothes on it that ended up with the foam attached to it so it was easy to shape the foam. And it made it soo helpful and very quick to make the pattern for the fur with some cheap scrap material when you can work off a dummy
and pin it right to it
If you go over to youtube you can see a lot of progress videos of different quad suits and see how other people did things - it's very helpful
Tiger just before he got finished http://www.youtube.com/watch?v=P-iL5RVfLwk
Tiger when he was "finished" lol still needs some work though http://www.youtube.com/watch?v=xJUXJ2FFIF8
Beetlecat's Targ (not a wolf but soo cool :P) http://www.youtube.com/watch?v=eyLkRCXjMyY
Koisnake already posted her guy :P
Hope that helps