For more information I refer to several blogs on CrazyGuy : www.crazyguyonabike.com/doc/categories/?o=Sh&category_id=378&doctype=journal .
There is also an extensive topic on Bikepacking involving the route's main architect, Casey Greene, that you may find helpfull : http://www.bikepacking.net/forum/routes/idaho-hot-springs-mountain-bike-route-2014-info-thread/
Solo or not? Last year I rode solo from Arizona to British Columbia on dirt roads and I don't see why you shouldn't do the main IHS route solo. From what I read in the blogs, the route is already quite popular. You'll probably meet other riders about every day. The singletracks are much more remote and wild, so that is a more serious commitment going solo.