I can't answer better than a native, but from a tourist's perspective, I spent 3 weeks, primarily in the Highlands, in May 2003. I chose that time of year on purpose because it was early in the season - the museums, etc, were open and the crowds were low. I hired a car and I had the single-lane roads almost all to myself. My traveling buddy (a 72 YO widower) and I also had no problems getting separate rooms (which you won't need) at the local B&Bs w/o having to make reservations. The only museum that had not opened yet for the season was the Village museum in Glencoe.

Also the midges don't come out until June. And, as you probably know, the heather won't be in bloom. But, the gorse and other plant life will have lots of color that early. Since this is your honeymoon, I also recommend that you take the wife.