Your level 3 will be fine to meet the requirements of Ofsted.
No EYFS, no medical, you may get a visit though I've been registered many years now and have not had a visit so it's pot luck if you get a visit or not.
If you have worked in a childcare setting in the same local authority area (or county) as you will be nannying in, then the safeguarding details will be the same - though you won't have a manager to go to with your concerns, you would go direct to the general contact for your area, or to the parents (if they were not a possible cause of the concern).
My unofficial guide to completing the Ofsted registration form
details about DBS checks - though follow any instructions given to you by Ofsted and please do let me know if they differ to what I have written.
Details about minimum holiday entitlement
As NomDeClavier says, it's the relationship between you and the parents which is different to working in an organisation. On the plus side, there is little in the way of office politics, no having to get on with lots of other people, but you have other issues that occur. Trust takes time to build up... they need to trust you and you need to trust them. It can be very lonely - no other adults to talk to during your working day. If your boss lets you, you can try to get to know other local nannies, local parents and grandparents, local childminders, and thus have other adults to meet up with at toddler group, at the park/playground.
I feel your biggest change will be that you are on your own, you need to think on your feet if something happens to you, your car, the children, the house. It's great when you find a family who you gel with, you can end up staying for many years. Be prepared for it to be different to nursery - at a nursery you may get a break, as a nanny you can't even go to the loo without a toddler following you!