See the attached image from the guide. Pin 3 of the audio video encoder, in yellow, is composite. Run the composite video wire to any of those points.
As for 3.3v and 1.8v, there isn't really any specific ideal place to put them, on any trim for that matter. You don't have to run those or ground to the specific points in the 4 layer documentation: those are mostly a quick reference. All the points of the same voltage are connected through a big voltage plane on the center of the board. So as long as you are connecting it to part of that plane, you should be good. You can connect it where you see several vias, or to the relocated tantalum capacitors.
Also, your U10 line is not wired up, so your system will not boot. You will also need USB wired up as well.
Additionally, your wires look pretty thin. Make sure you are using at least 22awg for your power rails.
Regarding your soldering, I would advise touching it up. The joints look cold and not properly joined, which can cause issues down the line. Some of your leads are too long as well. You also have some scary stray strands going on, like one from the B+ that looks like it's about to short out your lithium battery to b-.
For soldering, you want both the wire and the pad you are soldering to to reach the melting temperature of the solder. Using flux (external flux, more than just the rosin core) makes life so much easier. Soldering without flux is like washing dishes without soap: possible, but why would you want to do things the hard way? If you are using lead free solder, switching to 63/37 leaded solder can make a huge difference. And make sure you are using a proper temperature controlled iron.
The hard part of the more advanced trims like these is not actually cutting the board. That's easy. The hard part is troubleshooting. You need to have a pretty good understanding of the board to work through the issues. You will find members of this forum guiding newer modders towards the easier and more documented trims because they want you to succeed. We point out issues bluntly because we want to help you dodge common pitfalls rather than watch you learn the hard way. I do believe you can perform this trim eventually, but I think you may be bitting off more than you can chew right now. I recommend performing the standard trim as outlined in the guide, then trimming the board smaller from there once you get that trim working. Perform step 1 before jumping to step 2.
