How much spending money should I get?

slightly confused by what you're asking

yes, £4k/40 is £100, but there's 52 weeks in the year you're probably going to want to be alive for, unless you don't spend during the holidays

40 student weeks. I’ll get a job when I’m home. Well that’s the plan

then you should have more than £100/week to save or spend during term

So the full maintenance grant is just under £10k (assuming your parents qualify for it).

If they decide to take none of it, then the assumption is they match it.

So if halls accommodation was £6k, that leaves £4k. £4k divided by 40 weeks = a weekly spending allowance of £100. Is that about right

The maintenance loan is made to the student, not their parents. Household income is taken into account and if you have higher earning parents the loan will be reduced with the parents expected to make up the difference. Parents are not required to pay anything and many pay nothing at all or less than the shortfall because the can't afford to, leaving the student to rely on savings, part time job etc.

If your parents are wealthy enough to be able to fund your whole university living costs you are very fortunate. How much you need depends very much on where you go to university. Your accommodation budget will depend on where you go, what type of accommodation you are allocated - cheaper rooms are in great demand and you may end up being put somewhere you didn't budget for For example, UCL has single rooms as cheap as £138/week but also as expensive as £293/week both for 39 week contracts. Going to a northern university is typically cheaper than a southern/London one, and that will impact on how much you need to live on.