It really depends on the tire you’d like to put on it. If I were you, I’d probably go for a smaller inner width - between 32 to 35mm. Most of the tires we ride on unicycles should get on these width whereas a 40mm rim would probably be too large for some tires. For example, LightBicycle doesn’t recommend using a tire narrower than 2.8" on a 40mm rim:
Are you sure you want to go for ISIS? I’m not saying it is a bad standard, but I’ve heard it may become less and less popular for high-end unicycles. It is said that KH will slightly move to Qaxle… I have not got any due date or specs, but it may be great to think about that 
I’ll try to grab more info tonight 
It is not a bad idea at all. If the wheel is well built, you won’t have any issue and you’ll enjoy a light and reactive wheel. If it is a not well built… Well, you won’t ride it a lot of times before it breaks 
So, be sure you use correct spokes - double butted spokes would be great - and check the spokes tension.
I’ve seen some 2m-high drop jumped on a carbon wheel so they are well-suited for our sport
If you have any more questions, you’re welcome to ask them here. It’d be better to have them in a public thread than in a private chat as other people can read, learn and debate there.