Sadly no where near me so no help there! I'm with mostly London agencies and a few SW ones.
All good, all make you employable! I usually answer 'market rate' as my answer to the wage question!
Overnights would involve sleeping over. I go to bed when I would usually, mind you have only done it a few times. Its something only some families ask for so if saying yes puts you ahead of another candidate thats a good thing!
Having your own car is good for getting you to work, again makes you more employable. Even if I owned a brand new car I wouldn't use it for work. Having a licence makes you more employable in that the family can either provide you with a car or put you on their own car insurance, as I am now on my employers.
One thing they may ask about is Ofsted registration so may be worth reading up on it. Basically the only good thing about registering is that parents can use vouchers they get from their own work to pay you. You get paid the same amount, they save a little. You have to pay around £100 per year to register so if they ask perhaps say you are willing to do it but the parents have to pay as they are the ones to benefit, thats what I say. Though you may have to do an extra qualification to register.
Emphasise your good points! Happy to work with older kids, happy to do nanny/HK (I'd never do that so it sometimes limits my job prospects!). Having a degree is good news, as is SN experience.
TBH it is very, very unlikely they don't register you. the interview is to present yourself to them so they can 'present' you to their clients. The only reason I can see they may turn you down- some agencies require you to have had a 2 year employment with a single family before they register you. Which I would fail, my longest was 23 months as the family moved! Thats a rare requirement though.
One thing every single agency asks without fail is to fill in a form detailing all previous employment, names and addresses for references. Which you have to think up on the day. I take a list I did of all details, plus my CV which I find helps!
Wow I type a lot, can you tell I've done this a million times!