My husband has an very 'consuming' job too Robina, coupled with the fact that I am a teacher.
I returned to work at 3 mths, simply because there was no one to teach the A level class! I am glad I did as it allowed me to 'keep my hand in'. However, it was hard (even very much p/t) - I hated all the damn pumping etc. Childcare was expensive as I taught classes rather than days (live very close by). I did enjoy it though.
If I were to have another child I would have at least the first year off, if not two. I would feel more comfortable doing that because I am pretty sure the school would take me back, as I have proved to be so flexible and made having a p/t member of staff easy for them. With my first though, if I hadn't have gone back (I had only really just started at the school) I think I would have been in danger of never going back.
The deputy head at my last school (secondary) told me that she had 5 full years off when she had her kids - they were as poor as church mice (her words) but she doesn't regret it for a second. When she returned she was ready to go full steam ahead with her career (she is now on her second headship). It did help that her husband didn't have a particulary demanding job though (vicar).
Do you still have any contacts with your last school? Would you like to return there? If so, I would let them know that you would like to return to work at some point. There may be someone returning from maternity leave who would like a job share etc at some point in the next year or so.
If I were you, I would probably leave it another year. At least until your oldest is three. I would certainly list the costs and implications with your DH (illnesses, frequent when just starting nursery, housework etc).
I know that whether I returned to work f/t, p/t or I was a SAHM my DH wouldn't do anything around the house. I'm quite realistic about that now. I am working more next academic year and I will get a cleaner if I need to. Yet another expense!