How odd.
So you are cheerfully planning that in the event of a split, your DH would actually take every single aspect of your lives together, and you would be left as an entirely disposable accessory to your own family?
He has the money
the house
the children
employs a mum-substitute for all that everyday stuff that he's not there to do
...and you live in a one-bed flat on your own.
How on earth is this a prospect which fills you with anything but horror? It's just so - nothing. It's just a case of removing you from the family and replacing your spot with an employee. Chilling.
I don't imagine you'd feel positive about that kind of arrangement in the slightest if it actually came to a split. I think the reality of you living down the street in a bedsit while your children, husband and the au-pair had a jolly, busy family life just up the road, would destroy you: with you having to ask your children when they saw this film and how long have those socks needed mending and oh what school project was that? - 'oh it was weeks ago, did it with me Mum'.
That's without even starting on the financial setup here. I really do hope you don't split up, at least not until you have done some serious reading about your rights with regard to finances:
'DH earns 65k a year, I earn nothing (SAHM). We were talking about the proportion of DH's income which would come to me as child support were we to break up (have 2 DCs, 6 and 9). After talking some more we 'agreed' that it would make more sense if DH was the resident parent as he could easily afford an au pair or similar (it would be less than what he'd pay me in CS were I the resident parent), plus housing etc etc (we rent), and he's quite senior so works from home often. I would retrain (eventual plan anyway when DCs are a little older), and pay him child support out of whatever my income was - could afford to rent a 1-bed place but not the three beds the RP would need, etc etc. I know that maintenance would be payable(?), were we to seperate but we were talking about what would be in the DCs best longterm benefit.'
Stop RIGHT THERE.
He doesn't 'earn 65K and you earn nothing' - you are married, the FAMILY INCOME is 65K, for which he works outside the home and you work within it and provide childcare. In order to do this you have made serious financial sacrifices in terms of training, income now, and pension. The 65K belongs to BOTH of you.
If you were to split up, it would be more usual for YOU to stay as the resident parent, him paying not only maintenance but also spousal maintenance - essentially, paying for you to remain as the children's carer for the appropriate length of time, usually also in order to support you while you retrain. This arrangement is usually put into operation as it is recognised that the SAHP has sacrificed his/her job prospects in order to stay at home, so if the marriage ends they are left in the weaker financial position. Why the HELL should you live in a one-bed flat while your DH sits in the big house with your family around him? Why? Has he contributed more? No. Does he already have more advantages in place? Yes - he has earning power.
In the event of a split, more of the assets of the marriage generally go to the parent with care, and because this is usually the stay-at-home parent, the balance of earning power and advantage is thus more fairly distributed. Your thinking seems entirely naive - that somehow you are worth less than him, so you will cheerfully trot off and make no trouble, while he continues to enjoy the lifestyle THAT YOUR CAREER SACRIFICES HAVE PARTIALLY PAID FOR. If your DH were the slightest bit of a dodgy one, he would be smirking with delight at your suggestion here - that you basically leave the marriage with nothing and give him the children too.
Do some reading and thinking on this!