Don't do your needs in the open air, there are public toilets in the villages and if not, take a coffee or pay the service rental fee.
with your interests, you could find closed roads and may be surprised by the hidden corners
that Iceland has that weren't within your route. Go to small towns and observe the dynamics of people, stop in demarcated areas to appreciate the landscape
, listen to nature, take your time.
The mountain passes in winter often have strong winds and snow, so visibility is poor, go very slowly and check out my Tips for Driving in Iceland during winter.
If you are traveling with someone be a team
, especially if it's cold outside. Everything is done faster and better.
Communicate with your companions
, you will travel 24/7 together and people always have differences. The important thing is to know how to handle a conflicts and solve them so you can enjoy the trip.