How do I stay disciplined and choose the right skills to learn?

You are reskilling, which already puts you ahead of most, who only talk about it. What trips you now are two real things: staying disciplined when the newness wears off, and choosing the right skills when everything looks important. Both are common walls, and hitting them does not mean you are doing it wrong. It means you are far enough in to meet the real difficulties. Choosing well gets easier when you stop asking what is valuable in general and start asking what is valuable for where you want to go. Almost any skill is worth something to someone; that is why the open field is paralyzing. Pick a direction first, even a rough one, and most of the options fall away on their own. Discipline, meanwhile, rarely comes from motivation. It comes from a small routine you keep even on the days you do not feel like it. Choose one skill that clearly serves your direction and commit to a fixed, modest amount of it each day, small enough that you cannot talk yourself out of it. Consistency beats intensity every time. A little, held steady, will carry you further than bursts of ambition that burn out by month's end.