sorry but aside formt he money issue there you sound like you still want to be very much a part of her life - your thougths of what she should/shouldn't do are irrelevant really - you think she should rent - fair enough that's your opinion.
why exactly she would want to move to a bigger house I don't understand if she can't afford it on what she has. I understand the whole thing of better area/schools etc but still needs to live within her means. She should use her capital in the house and basically buy a nice one in the area she wants like for like.
You shouldn't be left with nothing no and £500 is a v v reasonable amount - fwiw I get a lot less than that and my XH is on your wages - and he has literally NO housing costs or elec/gas/council tax etc, so on that front you're v reasonable/generous and she's v unreasonable.
I'm assuming this split was only recently? if it is then you really need to work thru this - you need to come to terms with the new relationship which you guys have. (one which 16 months down the line i'm finally getting to grips with) If I were you i'd seek legal advice, and sort things out- a reasonable offer is for her to have say 60% of the equity and the maintenance you offer.
She will get her tax credits, and child benifit - tbh you're saying she should work FT - again your opinion, typically a lone parent is best off working PT and having the top ups. however this will obv usually only apply to renting not a morgage.
She needs to learn to manage her money and make sacrifices if she wants to keep her PT working you can't be expected to subsidise her living costs at the expense of your own.
oh and also to rent- basically that would eat into her equity capital as she wouldn't get HB if she's got a good level of savings - so yes good in theory but not so much in the long term iycwim.
sod - I used to hold you in high reguard but this line here '
dont be a sucker just cos she's doing the mealy mouthed single parent routine. i know plenty that piss their maintenance away. ' is WAY WAY out of line and you know it is. you're doing the men stick together thing.