Q2 Is this sort of route feesable in 2-3 months?
Yes
Q4 Do i need a carnet? if so for what countries?
No
Q5 Do i need to obtain visas in advance
Alg and ideally Mali yes, others at border
Q6 Can anyone recommend a good travel insurer based in the uk who would cover for this sort of trip?
Alg is FCO blacklisted so probably no
Q7 Can Third party insurance be obtained in the uk for the bike
No
... or does this have to be done locally?
Yes, but dont put too much faith in insurance, travel or 3rd party. You're on your own.
Q8 Is a guide necessary/compulsary for Algeria?
Yes.
Even with your reading and riding experience your route is pretty ambitious - not unlike my own first desert plans, but riding in the real desert the first time is quite a shock and keeping it together over such a distance will take some stamina and luck. Nema will require 4x4 support, M13 is a jump in the deep end (will know first hand in a couple of weeks) and Gao to Algie is not without risks. After that it's pretty easy.
See:
http://www.sahara-overland.com/country
It may sound tame but IMO tooling around in south Maroc (and maybe Mori) will still give you plenty to think about before coming back another time to tackle the big route with experience and confidence.
Ch