I was in Guinea about 2 years ago and can only echo what AfricaByBike says.
At that time there was an extensive road building program on the route from Bamako to Conakry - may even be sealed all the way by now.
In the Fouta the main tracks are generally OK - they're used by trucks. Take it easy and you should be fine, at least at this time of year and without much baggage. In the rainy season I think the tracks would be much more difficult.
I went from Kindia to Labe then to Koundara before Senegal - excellent ride. There's hotels in all these towns. The locals were very friendly and there was virtually no hassle. I think staying in a village would be no problem. Try to learn to speak a little Peul, although there's usually someone around who can speak French.
The only problem I had was the 'road' from Koundara to the Senegal frontier - very rough and the heat at this time of year didn't help.
Congratulations on doing this on a Mobylette.