The trucks on the road should be your least problem. At least I have found them to be amongst the most courteous drivers on the highway. Having said that, they tend to leave the city here in the afternoon and drive through the evening and night so there won't be heavy truck traffic when you are riding. What you have to watch out for is cars pulling camper trailers, those never seem to realize how wide those campers are.
Once you get around 100 km out of the city in any direction, the traffic dies down to almost nothing so you should have no problems.
The wind is everpresent and always seems to be in your face, strange as that may seem since there is no such thing as a straight road in Iceland...
Is there no room for fenders ?

Magnús Þór (don't know if the icelandic characters show up correctly.)
Ísland