Why so much rowing and so little stretching?
Because the front of most desk workers isn't especially tight, it's just that the back is weak and has no endurance. Stretching your chest feels good for an hour. Rows change where your shoulders sit all day.
Can I do this without any equipment?
Mostly. Wall slides, chin tucks, cat-cow and prone raises need nothing. A single resistance band covers rows and face pulls and costs less than a coffee and a sandwich.
How long until I stop having to think about it?
Around week 6 for most people, and it shows up as noticing you've been sitting well rather than deciding to. The photo comparison at week 8 tends to be more convincing than the feeling.
My neck is genuinely painful, not just stiff.
Then this is the wrong plan. Ongoing pain, headaches, or numbness and tingling down an arm are worth a professional's eyes rather than a mobility routine.