I know those back roads quite well and have cycled some of them by mountain bike. Due to the high rainfall this season stretches of these sandy roads will be swamped. Your biggest problem is the deep sand on long stretches. Best tip is to follow the tracks of local cyclists as they often detour into the bush to find the most firm ground. Most of the rain in southern Mozambique falls during January and February and another tropical cyclone is unlikely. So yes it is a bit early for ideal conditions, and if you can delay until April the roads will be firm and not swampy mud and the weather will be cooler. Note that a tent is highly recommended as there will be lots of mosquitoes and few places for visitors to overnight.