Orcs was monsters in Beowolf who was one of the inspirations for Lords Of the Ring.
Hobit is an Tolkien invention and is copyrighted, halfing is the public version.
TES elves are more like the Tolkien elves than the mythological ones as both is actual races of humanoids, however the TES version is more like humans, much the same for TES Orcs.
For dragons, an four legged one might actually be easier to animate on ground as its an normal four legged creature, however the long tail an neck might create problems.
The proportions however would create lots of problems.
For one we expect an decent amount of wing area, yes the dragons in Skyrim has to small wings to fly in real world, however twice as large would create problems while half as large would look fake.