You've had good advice here. Remember that some things are important (shopping within a budget so you eat well but don't go bankrupt) and some things are less important (which hoover to buy - as long as it works, is within your budget and gets the crap off your floor, the rest is irrelevant. My £30 Tesco own brand hoover won't be winning any Good Housekeeping awards for best appliance any time soon but it does the job). Prioritise the important things and learn to accept 'good enough' for everything else, it saves a lot of stress.
I wouldn't get your MIL to organise it all, because I think it is important that you make this new place yours. Think about how you would like it to be. Then think about how you're going to make that happen, and ask your MIL for help on the bits where you're not sure how to do it.
I would start simple - fill the house with essentials, and then, as you're settled, add more stuff in if you spy a gap or a way to make life easier, so:
Bed for you & DP, bed for your DC
Bedroom storage space (wardrobes and chest of drawrers for clothes/socks/underwear, some form of toy storage for DC)
Clothes airer
Sofa to sit on
Table to eat at
Cooker, oven, kettle, toaster
Fridge, freezer, washing machine
Storage for books/dvds etc if you have lots
Curtains (if not provided), towels, sheets
This is what we did when DP and I started out in our own place (well, minus the washing machine actually, which was a pain in the arse and I nearly cried with gratitude when my parents bought us one after 5 months of lugging everything to the launderette in the next town). You then find yourself thinking, after a while 'ooh, wouldn't it be handy/nice if we had a thing to do x' and you find yourself buying a shoerack to stop the pile of shoes in the hallway, or some potted plants to cheer up the living room, or a little table to sit the printer on because you keep tripping over it on the floor. That stuff is all secondary, and it'll come.
Mealplanning - I make a list in two parts: one with the days of the week, what I want to eat which day, and what ingredients are needed that I don't already have in the house (so it might say 'Monday, mushroom risotto - mushrooms, onions, stock cube, cheese' but no risotto because there's still a pack in the cupboard) and the second part with 'general' stuff that's needed but not for a particular day - so looroll, bin bags, milk, bread, snacks. Then I go online and order the lot of it because I hate going shopping and I always spend more than I mean to if I actually go in.
Cleaning routine - umm, my house looks like a bomb's gone off so I'll leave that one to someone else :o