Hello,
Just returned from the same trip onboard a Tenere, here's what I found:
1, It took me two months to get to SA then I toured around SA for a couple of weeks before CT.
2, I had no visas on departure. All obtained a country or two before or on the border. I had an existing carnet from a trip last year.
3, Cost me in the region of €3000-€3500 for what you described. Main cost 'on the road' was the visas. Some were up to €100 a go, all seemed to depend on when and where they were purchased.
4, I rode down to Dolisie, turned right for Pointe Noir, then Cabinda. No problems.
5 & 6, I'm not an expert on this, plenty of info on here though. I had five pages and came back with an unused page, others claim to not need one while others will use one all the time even if it's unnecessary.
7, From memory around 250 miles? Maybe someone will correct me on that. However, I didn't take spare fuel and my bike's range is up to 300 miles and I didn't have a problem.
8, Haven't done the east coast but like everything on here there's many many different opinions and things are always changing. Remember though, my experience could be totally different to yours along the same route. This is Africa...
More info here if it helps...
Ian's RTW trip
Good luck!
Ian