Hi,
Al tips above are great, and are ones that I considered when working part-time.
Depending on your work and how important it is to you, I would recommend putting the focus on what works for your employer and (internal) clients. After all, you want to be able to show you are still contributing meaningfully, and you don't want colleagues to give you less work because you are 'never there'.
I did 4 days, being home on Wednesdays (and still available for urgent messages). It worked for me, as that way anything urgent could be done before the weekend. It also helped in making me feel more part of the team, and keep a 'work' mindset. That last one was important to me, as somehow when you have been a few days away work just doesn't seem so important anymore, and the quality I would deliver would have suffered.
So it depends on the type of work you do, and what it requires, and what your colleagues can more easily cover for you.
I don't think it makes a huge difference for the baby, babies need a loving, responsible person in their lives they can bond with and that helps them feel safe and secure. Consistency is important, but as you will be there nights, mornings and evenings, and you are thinking about a regular nanny that should be fine.
After the recession has started I have the impresion nannies seem to be a lot easier to come by, but perhaps I (and the people I know) have just been lucky. I do know nurseries are struggling to fill their places rather than having waiting lists.
Also check out some more considerations on my website Mum & Career
http://www.mumandcareer.co.uk/category/ ... g-it-work/
All the best, Inge