stock up on advil for him (those first few weeks are gonna be interesting).
don't assume the house will look upon your return anywhere near what it looked like when you left it (you may find yourself doing alot more big cleaning unless dh is good at picking up after the kids/himself as he goes along).
maybe bribe the 8 year old to take on some extra chores that might initialy get set aside in the wake of the 'evening managment change' (like putting the dishes in the dishwasher, putting the leftovers away, putting laundry away....).
i know this sounds totaly goofy what with dh being a parent of children and around them all the time-but you might want to grab a copy of 'what to expect-the baby years/toddler years' for him to have on hand. i've known dads who were awsome but when left alone with a baby the most basic things baffled them-having an 'owners manual' to refer to might not be such a bad idea (and might save allot of needless calls to you at work). you might also want to make a quick reference notebook of where you keep things he would'nt usualy have much need to look for-spare bottles of tearless shampoo, extra baby wipes, tweezers, nasel bulb (teach him how to use it-not a great thing to have to trial and error with a fussy baby), humidifier...
anyone whose not pottytrained-i'de do a double bedding on. sheet covered by waterproof sheet, covered by another sheet, topped with waterproof sheet. unless he going to be realy willing to change a soiled/wet bedding it could keep you from ending up coming home to the younger ones 'snuggling with dad' in your bed-because 'we were both tired and it was easier than tearing that bed apart to change the sheets'.
good luck mom!