Let's take this moment to grab the four codex pages and the one seal, if you didn't grab them already.
Codex Pages 3-7
East - Go east, to the NE city exit. Toss money, go in, and then run out to evade.
Southeast - Just toss money and go in, then run out.
West - These guys didn't fall for the money, so whatever works.
Northwest - Another room that wasn't allowed entry with mere coin.
North-middle - Will be hidden if you bought the treasure map, so zoom in to see it.
Remember to lower your wanted level by tearing down posters, which tossing coin helps.
Il Duomo's Secret
Enter the assassin's tomb in almost the dead center of the map you can see. Then entance is on the wall of the church.
Climb the little seat you saw in the scene, climb up the slashes in the wall, and then get to the other wall at the windows. Jump to the chandeliers, then to the wooden board where the pigeons sit to the other chandelier. Jump to the south wall for a quick scene to mark your progress in case you mess up.
Go west, up, and then back east. Keep going, then move out onto the pole to jump to the smaller chandeliers. Don't rush the second jump, and get to the pillar platform.
The pigeons point you to the chandeliers to the other wall, the stone platform by the window. Go up and east, to the chandelier, and then south all the way to the opposite wall. Go east, and just jump off the second pole to land on the wooden walkway to drop a second safety ladder.
Now you need to circle around the walls, so from this walkway jump to the ring of pillars, and follow the pigeons to reach the other side. Jump back to the ring of pillars, head down, and jump to the floating platform. Jump left and go up, then follow the path to the pigeons under the stained-glass window to start climbing up.
Up top, jump to the wooden boards, and follow the path to a pole that drops you down a little. Jump the chandelier to the stained-glass walls and climb up the east side to get up. Jump to the boards and perch on the piece pointing south. Follow the path over the floating board to the west and up the ladder.
Now just follow the wall all the way around to the end of this walkway where the camera changes angles. Climb up the bricks and that middle board is the destination. Get up, look to the middle of the roof, and jump.
You know the routine, open three chests then the tomb. Open the window on the side to exit.
Two chests out here (and only grab the feather if you physically write down somewhere that you got the Duomo feather), then jump twice over the SW rail to hit two hay piles in a row.
Lorenzo offers the first mission of this memory sequence in the northern parts of the city.
You got a Medici Cape, making the orangish guards more friendly to you, but red guards are the same. Tailor just to the west of here if you want to match colors with the pizza cape; nothing matches it.
Enter Da Vinci's house.
That's the mission. Now the side missions will be back on the map, in case you feared you missed them. Feel free to do them now since you don't want them hanging, but they suck up a lot of time. Side missions consume a ton of time, so I won't cover them in the walkthrough.
I would advise checking the tailors for dyes if you want, which are different from the ones in your villa. And then buy up a few paintings from an art merchant if you want. If you need quick cash for the paintings and have done no side missions, feel free.
Before we leave, make sure you have the codex's, viewpoints, and the tomb.
May be faster to use Da Vinci's travel station to get to your villa, collect and do whatever, then travel back to Florence's East Gate.
From the East Gate, ride a horse north out of town to the Mountains.
Started upon entering the Mountains area.
Lots of things to deal with here. First is steering. Turn too sharply without giving a little to the turn will result in a rollover and fail. As well as avoiding the obstacles and eventually fire. You can't crash by hitting a wall, but you can cause damage to the carriage, so avoid as much as you can.
Second are the enemies jumping on. Only extended walls can knock them off while they are on the sides. If that fails, you have about four seconds to swerve the carriage to and fro to unbalance them to knock them off. And finally you can just mash the melee button when they get to you to quickly knock them off, and the carriage does not go into complete auto-pilot, so mash fast.
Third is the damage done. Fire doesn't do much, but it adds up, and some obstacles can be run through for a small fee of damage. Also, if you can, knock off guys using tree branches.
After the ride, just defend a little and then go to the marker. Again, don't fight them all day, you don't have to.