So on a Spousal Visa, I pay the NHS surcharge and keep doing it every year?
No, you just pay the full amount at the time of your visa application. It's £200 per year of the visa, and as the spousal visa is 2 years and 9 months, the amount is rounded up to 3 years... so as part of the visa application, you pay £600, which covers the whole length of the visa.
Then, when you apply for the next visa after 2.5 years, you pay it again... this time, £500 as the visa is 2 years and 6 months (2.5 years x £200).
Does that entitle me to the same NHS treatment as everyone else? I'll be in Scotland if that matters. (I recall something about prescriptions not costing anything when I lived there but not sure).
Yes, that entitles you to the same NHS access as UK citizens. If you live in Scotland, all prescriptions filled in Scotland are free.
What about my UK wife who has been out of the UK for more than 10 years. She is worried about some habitual test or something.
What about our 2 kids?
If they are all UK citizens, they will also be entitled to full NHS access, as long as they are making the UK their permanent home (i.e. they aren't just visiting).