Hi Esteban,
like you say, roads nearly all the way so I would stick with the comfy V-Strom you know
I rode to RIM border last year:
https://sahara-overland.com/2020/04/...antic-highway/
I think a 250 Domi would be agony unless you are a Zen monk.
Longest piste will be to Diama, if you go that way.
For the CdP and visa for Senegal see the sub Sahara forum.
I think all visas are at the border. Certainly RIM.
https://sahara-overland.com/mauritania/
With vax, I am guessing Morocco would be most strict.
So south from there 2 may be enough.
I would not bother with malaria pills for a quick ride to Dakar. Just use spray and a treated net, if needed. I imagine December will be mosquito low season.
I think Guinea could be an adventure and you may have time and energy.
See how you feel in Dakar then get a visa.
bonne route