I went with your advice to grow to Size 4 with the third work boat.
Turn 35 - Road complete at (1,1).
Turn 36 - Settler 1 in Thebes. Move to 1,1.
Turn 37 - Road complete at (2,2). Found Memphis at (1,3).
Memphis grabbed the clams, so I micro'd Thebes to work a Forest tile. The horse pasture will be ready in 4 turns.
Memphis is growing to size 2 and I decided to grow on a warrior. I will need one soon, anyway.
Turn 38 - Start the horse pasture at (0,4).
Turn 41 - Work boat complete. Move to (-2,1). Horse pasture complete at (0,4).
When the copper showed up, I suddenly got cautious with that warrior and did a bad job scouting. At this point, the warrior should just go back to Thebes and fortify. The barbarians are coming - and so are the war chariots.
For Micro, Memphis can make it to size 2 in 3 turns and complete the warrior by working the horse. I thought it was better to work a horse title for 2f, 3h, 1c in Memphis than to work a forest tile in Thebes for 2f, 1h. When it hits size 2, then I can whip the granary in Thebes and have 17 hammers towards the war chariot.
Added: up to Turn 46
Since I had an even number of commerce, I ran 50% treasury to raise some money. For Turns 42 to 45, I had 20 commerce and could set the treasury wherever I wanted, so ran 90% for a couple of turns and 70% for a couple of turns. The treasury is now at 44 gp. We have events on and some events cost money. Right now, most events cost 20 gp.
Turn 42 - We have the clams at (-2,1).
Turn 43 - The Zulus founded their second city, just two turns after we did.
Also, the road is complete at (0,4) and we have access to Thebes.
There is not much else to do around Memphis, so the Worker will return to Thebes.
Turn 44 - Warrior 2 is ready in Memphis. It will defend. Warrior 1 will defend Thebes.
Memphis also grew to size 2 and is working the clams and horse.
Thebes is stuck working a 3h tile.
Turn 45 - Thebes grew to size 5, so we switched over to slavery and whipped the granary.
I waited on this, because I wanted Memphis to be size 2 to work the clams and the horse.
Thebes is now size 3 and works the other clams, fish, and pig iron.
Our first War Chariot will be ready next turn.
This seems to be a huge improvement over my first try at this. We have our first War Chariot at Turn 47 instead of Turn 55.
From here, I have not decided whether I am better off starting a second worker right away or letting Thebes grow to 4 and then do it. With workers, earlier is probably better and we get only one hammer at size 4. I might even do better to build the second Worker and wait on the War Chariot. I will think about it.
Also - what to research next, Sailing or Writing? For warmongering, neither is really helpful. The Sailing will give us another building to whip, the Lighthouse. Writing gives us the Library. It also allows open borders with Shaka and I would get to see his empire from the inside.
We still have options open on early war or early expansion.
Added: up to Turn 53
I went with Writing. Then we can check out Shaka more closely.
I changed the build in Thebes to Worker. I figured it would be more useful at this point and the payoff will be quick. There is a little bit too much for one Worker to do.
Turn 47 - Forest chopped on the green hill.
Turn 48 - Worker 2 in Thebes.
Meanwhile in Ulundi, the Zulus have truffles.
There it is! They can put a mine there and have a tile equal to our pig iron mine! 2f, 3f, 1c. It isn't game breaking, but it seems pretty big.
Turn 50 - Memphis grows to size 3. It is now working the clams, horse, and pig iron. Thebes is stuck with a 3h tile.
Turn 51 - War Chariot 1 is ready in Memphis. It starts rolling towards Zulu territory.
Elsewhere in the world, somebody built Stonehenge. This is no surprise.
Forest cleared. Green Mine complete. Thebes grew to size 4 and is still stuck working a 3h tile.
Turn 52 - War Chariot 2 is ready in Thebes. There is another decision point I could have stopped at, what to build next. The option is still open to build a settler and found a city by that seafood.
Turn 53 - Writing. We signed open borders with Shaka and rolled War Chariot 1 in to get a proper sight on Ulundi.
There are three archers and a settler in Ulundi. The other stack is an archer and a warrior protecting a worker. mBgungunlovu is most likely somewhere to the southwest. It probably has at least two archers. They will have other units somewhere, because there is a reason they got ranked as most powerful and the strength ratio is persistently very low. They are also getting ready to settle a city somewhere.
What to research next? I have Sailing selected, but can switch to something else pretty quickly. Would a beeline to Construction be a good idea?
What to build in Thebes? I am leaning towards a Barracks. A Library would later give us an option to run scientists. A settler one turn ago might also have been a good idea.
Memphis will whip a Granary when it hits Size 4.