stressed - I'm in Middlesex so close to you.
If you look at the home page of Au Pair World and look at the UK Au Pair programme, it gives a lot of information about what is expected of an Au Pair and what they get in return. However, to give you my POV, I currently pay AP £65pw for 25 hours - she wanted a lot more but I said we could offer her a stable/loving environment where she will be treated as one of the family. She was happy with this. In fact, what they don't know is that I always offer low and then give them a bonus everytime they go beyond the call of duty. An old AP always used to be so happy with the extra bonus that she'd dance to school and tell my CM how nice I'd been.
You need to work out what you expect them to do - some will not like too much cleaning - if you need a schedule to base yours on, CAT me and I will send you mine. In terms of babysitting, we always say up to 2 evenings a week but average is once a week. However, be explicitely clear that this is included in the pocket money - I had an AP turn up and noted every hour she had helped (inc babysitting) and wanted payment for these. Some employers offer extra money for overtime, I don't instead I offer lots of time off. For holidays, I offer one week for every 6 months with us and, if they stay a year, an extra 2 weeks holiday as a bonus. I never pay for their flight home unless they stay til the end of the contract.
My AP goes to English lessons for 2hours a week, two days a week to Uxbridge College - it has cost me £160 plus £36 exam fee. I also pay her tube/bus fare there/back. Many moons ago, we wanted a car driver but were so nervous about them driving over here (as they are as well) that it just wasn't worth the extra hassle. Now we supply a bike.
We always give our APs the weekends off but most of their friends have to work Saturday so this varies from family to family.
Initially, we had APs dfs/family over to stay in her very large en-suite room and it worked well. But with each new AP we have found that our hospitality is being taken more and more for granted. Now we say that no overnight visitors until at least one month after they start. And then, we will need to meet them and they can only stay when we are not there, with our prior approval.
I was very much like you initially, but I have really hardened up after a few disastrous experiences. In the same respect, you will find a lot of APs that have had an awful experience with a family so are looking for a "family" not a employer. Do not drop your requirements just because you are fed up with the recruitment process - you will find someone who is a perfect match eventually - you just have to weed out the timewasters who want to come to London (Herts is close enough) to go clubbing and meet up with their dfs.
I do know of a couple of Finnish girls coming in August, but I know you need someone now (by your name )