Hoid was a Dawnshard at some point in the deep past, and the reason he (even still) cannot physically harm people, or even eat meat, is related to the changes this made to his spirit. (Consider this the same fundamental principle as savanthood.) The few of you who have read Dragonsteel know that him being a Dawnshard was also the source of his immortality in that book, though the terms were different back then. (The word Dawnshard was never mentioned, for example--though the primary story of Dragonsteel (which is no longer cannon) was about several people who unwittingly become Dawnshards.)
And a preemptive RAFO to all questions on this point. :)
The Sleepless are one of the very first fantastical races I developed, and they made an appearance in Stars' End (my second--very bad--novel, which never was published.) I migrated them to the Cosmere after I started designing it, as I wanted some truly alien species. I was interested in an entity that could have "generations" within its own swarm of beings, breeding to evolve parts of its body, and spreading consciousness across a large number of individual pieces. I'd seen a lot of hive minds, and some group minds, in science fiction--and wanted to play with something that was a hybrid between the two.
However, in order to properly integrate them into the Stormlight story, I decided to make them be able to imitate humans. (And through these efforts, they are slightly more humanoid in the way they perceive the world.) That made them able to play in the events of Roshar more directly.
There are plenty of swarms in the cosmere who are not connected to those on Roshar, however.
Huio is based, partially, on someone I met while touring. I had a driver who was from Pakistan, originally. (It's not uncommon for the publisher or convention to assign me a driver to get me to all the places I needed to get.) We had a good time chatting, and I discovered he had a Ph.d. in mechanical engineering. However, for various reasons, his life in his home country was really difficult--so he took the chance to start over in a new country with a new life. (More, he wanted to get his children out of a bad situation. I believe he was Sikh--though he might have been Jain--and his family was suffering some persecution for it.)
He couldn't get work as an academic, despite being a professor, as his mastery of languages was really bad--and couldn't teach in his new country. He couldn't get a job in his field either, since both the language barrier was a problem, and also he had trouble getting businesses to accept his credentials since they didn't think highly of the programs in his country. (At least, not the ones he'd attended.)
So here was this man who was obviously WAY smarter than I was, doing an entry-level job. And he considered it an upgrade for certain personal reasons, but I could tell he was really frustrated by the language holding him back. I've always remembered the experience, and the lesson it taught me about assumptions I sometimes make.