20 years working in industry will set you in good stead. You will be used to working long hours, have attention to detail, work towards specifications, take pride in your work, schmooze bosses and clients, have excellent time management skills, etc etc etc.
A chemistry degree sets you up for A-level chemistry teaching, obviously, and there will be a few areas for you to learn, but not too much. You'd be expected to do two, if not three, subjects for GCSE, but these should not to be too hard for you to get up to speed with. You won't have all the anecdotes the first year, but will build up your repertoire. You can go to town on your industrial experience, especially towards the girls, as a role model.
I don't think you should dwell on too much negativity, other than to be aware. No workplace is perfect. A lot of the challenges can be in peripheral areas, such as photocopying budgets, and you learn to work around these,.
It is a funny job because you are it when you are in the classroom, but you have to work as a team with your department to share ideas, resources, and operations. You can do it on your own, if you are superwoman, but it's much better to work as part of a team.
You might find that a school hierarchy is more top down than you are used to, and be unlucky to have a "little Hitler" as your department head. This can be hard when you are mature and experienced in life. You just have to be strong to your own principles. It is sad that a lot of people in education think that an authoritative style of leadership is effective with fellow professionals.
Do some work shadowing in 2-3 different schools.