I think most of us have been in the same position as you and there is no perfect answer I'm afraid.
A couple of things I'd be careful of...
Your baby is constantly changing and developing. At around 6 months they start goin through separation anxiety but she should be through this by 12 months old.
Also, you want your child to gradually become less dependent on you emotionally so a couple of hours or days apart might be a good thing for both of you.
It's really difficult to make this decision whilst you're in the thick of it at home. It's too difficult to try and make an unemotional, rational decision when snuggled up with your little bundle of joy!
From your post you sound as though you really enjoy your job and you've managed to negotiate a job share so in both those respects you're very lucky. If I were you, I'd give it a go for a few months and then you will be able to make a more informed decision about your future, but you won't know until you try it.
If you go down the nanny route then I wouldn't worry about your husband putting his job first. Build up a good relationship with the nanny where she does breakfast if you need to get in early and she can babysit on parent evenings etc. Nannies are much more reliable and flexible than husbands!