Old Chum..I built and live in a log house. My best advise, if it is your dream home, go for it, but be prepared for a lot of extra maintenance. You need to treat the logs every 3-4 years, there is always shrinking and swelling going on due to the weather. Doors don't always close just right. Since you are looking at a kit home, you should't have all those quirks. Mine is built out of hand peeled and scribed logdge pole pine.
As far as R-factor for insulation, as long as the log joints are tight, the log will far exceed the insulation in a stick home wall. You'll just be hard pressed to find anything on paper. There are a lot of log home books and magazines out there whith some pretty good information. Read all you can, then make your decision
Good Luck.