@Archduke:
On some map (and this one looks like it is one of those) the GLH is really over-powered.
GLH is of course better with foreign trading partner, but national oversea routes are 2gpt immediatly which is more (?) than foreign inland trade.
As timmy wrote, having the GLH, eachtime you settle an island (up to island #3) you gain +6gpt from trade in the island city and +1gpt in each other cities if you have more than 3 cities or +2gpt per city if you have less than 3 (so easily +10gpt).
(and since we have not explore, we might find some other AIs not far away).
I am not against rushing, but I don't want to miss GLH.
I would still revolt to slavery, the capital has lots of food, and will regrow quickly without granary. The main problem will be happiness, but we could (if we have enough 'free-worker turns') connect gold and ivory.
I would whip some axes, and if we go GLH soon I would whip the (regular) lighthouse as well.
Even if we don't rush Shaka, I think we need 3axe which could be done quickly with 1 chop & 1whip. 3 axes will give us an option to raze a secondary city (if there is one) and if we are catching Shaka unprepared, we could always have a chance (ie only 1 archer and warriors defending).
Added after edit : If we just 'choke' Shaka, with 2-3 axes, disconnecting his metal/horse asap, pillaging everything, and 'camping' outside his city in wood, he won't be able to do us any harm and won't interfere with our plans.
For city#2, with pigs and plenty of hills, it could be our military provider (that was my idea anyway in the 'capital -> Wonders'), so it could build barrack (?) or axes directly to finish Shaka, another option is a galley and/or settler.
Long term, I agree we need more info about the surroundings (and AIs presences), but we will need a very strong research city (with GLib I guess).
We should also have a GPP farm (possible with Caste System and lots of Scientist to lightbulb up to Astro ?), which could well be the city on the marble. With 2 plain forrest and a plain workshop (?), it will have enough production to (slow) build the basic infra before recruting specialists. (before being in caste system, just need to build/whip granary, lighthouse and if possible library)
I am also more and more 'in love' with AP in my 'isolated' games, (oracling theology if possible) to get (1) religion, (2) the production bonus and also (3) to deny all its powers to the AIs.