Hmm... I think for the head it would be of a make similar to that of a fursuit, as well as the majority of the body. The shell most definitely could remain rigid to achieve a realistic effect, and the armor-making method you have employed with Zant and other projects would suit it well if you do not want to experiment with something new.
Connecting the two together will probably be one of the more difficult tasks, as I imagine you would want to zipper up the back where the shell will cover it. Perhaps a series of ties on the exterior of the suit and the interior of the shell can properly secure it if you do not want straps/velcro and the like.
I personally make my own wire frames from scratch for rounded forms, but have become intrigued my foam carving (I have seen it used to great effect on armor, as it can be sanded, gessoed/mached and finally painted while remaining quite sturdy, smooth, and light).
A fursuit tutorial would probably be the most useful information you can acquire at least for the initial yellow base suit, claws, stomach, and head (fortunately the wrist bands he wears could cover the edges of the sleeve/glove separation if you want to have them made apart. This would cut out labor and make it convenient to take off the hands if need be.)
That hair is crazy though!
You would have to leave a hole in the dome of the head to allow the hair to pass out of it from the inside, probably about a structure that will help it keep its shape.
Hope some of my suggestions help! I was interested in attempting a fursuit/mascot project myself, but have too many characters make in the meantime, lol.
P.S.: I've always loved your Legend of Zelda cosplays!
Keep up the good work!