About the harder and the hardest, it demand great technological progress, creating or modifying a body is hard, we don't fully understand genetic structure and genes. We know how it work, but not how to create new one or modify them (well, yes we actually can, but just a few, not enough for a new body with brand new genetic). So let's suppose we will modify our actual body, because this one already have functionning organs and muscles, it's a nice start, don't you think ?
So yeah, it could be done, but how much would it cost at first ? Probably hundreds of millions dollars, that a bit expensive
But let's say we have mastered this technique and now it cost "only" about 10,000 $ (still a bit expensive but it's better). Some Furrys would have it, and would be able to test this new body. Well a modification like that is not easy to handle, our brain will be lost, if you use digitigrade legs, the walking will be different so you may need reeducation. Then, if you have a new nose and a new pair of ears, capable to hear and smell better, your brain may not be able to process thoses information (I'm not sure though, I'm not a neuro physician). Okay, so you may need reeducation, and some time to be used to the new sensations.
Then, once you're out of all this, you understand the main problem : people.
You are different from other people, they will fear you because you're not the same, they don't understand what or who you are, so they will be most likely to hate you. Most of the people will treat you like they did with the black population about 200 years ago, you're not like them, and difference is not something people like.
After that come the second problem : pretty much everything is not ergonomic for you.
Maybe you won't be able to drive or pilot anything with that kind of legs, pants are not made for you if you have a tail (and many of us would have one), and my most feared problem : How the hell I am supposed to use my headphones
And since people don't like you, manufacturer will probably not produce anything for you, so you will live with that problem for a long time.
Until you launch a revolution and slice some heads off (not the kind of the community I must say), you will alway have thoses problems.
Beside all that, that would be awesome