The longbowmen mopped up Louis's inital stack, as was becoming routine. Experienced longbows promoted to Combat III and Shock (plus one natural first strike and free Drill I) had no trouble with swordsmen, and the good old Holkans handled chariots.
I captured a city from Louis...
... and bingo, that's exactly what I wanted. Pizza slice #2 acquired with hardly any bloodshed. And plenty of time to recycle my longbows against yet another target before anyone else gets a peer unit.
The bottom of the tree is my clear tech path now: Machinery (add crossbows to the mix) - Guilds (Knights!) - Banking (Mercantilism and banks both big.) Also in the meantime I traded for some ivory from Sitting Bull, and added a couple Elephants to the mix. Isabella had HBR so horse archers were a bit worrying.
And Mansa came to me of his own accord, offering to vassalize! Free pizza!
Now I can get truly manipulative. He's currently researching Literature, so I let him finish that and flip him Metal Casting for it. Hooray Heroic Epic. Then I make him research Machinery, for which I'll trade Feudalism -- while I save cash for a deficit run on Guilds.
Nuts, contacts are getting around more than they were supposed to. I guess vassals automatically contact their master's contacts. Oh well, may as well open borders to both my vassals so they can think about helping me in war against Isabella. A bit later on, everybody had contacts with each other, despite me never opening borders. So spy units must be able to make contact despite being invisible?
So I advanced my stack up to the first Spanish city, and...
... holy crap, that must be the stack she was trying to use against Sitting Bull but couldn't get there. Well, that is a forested tile, and most of the longbows are Shock, so I should be okay...
... so of course, between turns, the stack moves away and leaves three archers in the city that I easily paste.
But then on the NEXT turn, the Isabella AI did attack my stack. I won more fights than I lost, but the sheer numbers carried the day and now I had no more longbow army. (I did retain enough to protect Chichen Itza.)
Also, Isabella blew up her EPs in blowing up a farm, which let me see her research. Sure enough, Feudalism. OK, so I'll have to retrench and come back with knights. I waited out the cold-shoulder clock and then took her treasury for peace.
So my opening strategy was the greatest slingshot in the history of the game. 
With the Feudalism sling and ensuing longbow rush, I: resisted a three-civ dogpile in BC years; conquered one civ; vassalized two more; traded it for another key military tech, deficit-researched all the way up to a third dominating tech in Guilds, and traded that for Engineering thanks to vassal pet Mansa.
From here, the rest of the game is mostly going to be a formality. I won't lose now. Actually, with the two vassals, I'm already more than halfway to the domination limit! And my economy has recovered to 30% research and rising with ex-Russia as my breadbasket, which is solidly sufficient. (Really, all you have to do is not fall a generation behind in military tech. I'm getting knights which don't get stopped until grenadiers or cuirassiers.)
I'd quite enjoy using the knights in my next conquests. It's a rarity to really get to use them well. They are strong, but suffer from several problems: two counter-units (elephants and pikemen), inability to get City Raider and Cover, and they lie in an awkward area of the tech tree. Guilds requires two other pricey techs with no economic benefits in Feudalism and Machinery, and all three are hard to lightbulb and off the Liberalism path. Knights aren't strong enough to take cities all by themselves; they need siege backup. And if you're going to wait for slow siege, you may as well use macemen and musketmen which are cheaper and get better promos. This thread explains it all well. But things worked out well for knights here, having slinged Feudalism and traded it for Machinery, and with tech going slow enough that several enemies lack Engineering, and Cuirassiers for me would be quite a wait.