I've just gone back and read the thread again, and this jumped out at me:
DH taking paternity leave would sort of defeat the purpose
What did you mean by that?
And you say that the assignment will take 5 months - do you have any way of influencing this, so doing it over a shorter period of time, or is it calendar/date-specific, meaning it would have to run for this length of time?
If you have a bad week, and don't manage to fit in your 16 hours, would that matter? Could you catch up in a following week?
How much holiday does your DH have? Could he perhaps take a half or one day off a week to look after the baby so you can have a solid 'block' of time?
Are you prepared to consider formula feeding? Personally I'd have hated to do that, despite the issues I had getting going (both times!), but as PP have said, expressing is really difficult to achieve before your milk supply is established. And the obvious advantage of formula feeding is that your DH can share this with you, so he can do some of the night feeds - allowing you to sleep a bit more, so that you can be intellectually sharper. It would also mean that he could take the baby - possibly take it out for the day/afternoon, so leaving you in peace to focus on your work.
You talk about your mum flying in - so obviously she's in another country. Is she able to come again, a bit later on in your leave, for another block of time?
I can understand why you want to take this assignment, but I think you need to think a bit more about how you are going to handle things, rather than just hoping for the best!