Ooops you are right, it should have been “Generally the roads in the north are stony and can manage a lot of water; the roads in the south consist of more soil and can be muddy, but usually they dry up pretty fast.”
The temperature was normally 15-20°C, a bit colder at night.
The rain might hinder you to go some roads it depends on your vehicle, your skills and your route. For me it was no problem and the roads in Ethiopia are slow anyway. They tend to be filled with people and goats.
Like your friend say it might spoil some of the view but usually it doesn’t rain for more then one hour every day so it’s not that bad. After all the rain makes the vegetation even greener and the soil even more red so the view is fantastic!
I have not been to Ethiopia beside this trip in July-August and even if I don’t like rain I would like to go again. The temperature around New Year should be a bit hotter and much dryer. Maybe November is the best time, pretty dry and lots of colors.
It’s a terrific country, but the locals will test your patience to the limits.