Congratulations!!!!
Yes to decluttering, do not under estimate the amount of shite things small people have/want/keep!
Cot and bed (I also found two sets of bedding and even more fitted sheets were essential for those middle of the night pooplosions/puke! The mumsnet patented set up of bedmat/sheet/bedmat/sheet is a life saver when they're ill as you can whip one set off and have another already there.
Car seats/booster seat.
Calpol etc, mine seems to have an eternal cold/virus/sore throat. A little first aid kit geared up for kids is also helpful.
I asked FC about nappy size and brands and bought a few packs each week so I had a stash before placement. Ditto for things like shampoo and bubble bath so they smelt familiar (and laundry detergent to wash their bedding in as familiar smell can offer comfort in this early weeks).
Also ask FC about shoe and clothes size and how close they are to moving up to the next. My boy was just fitting his current age clothes so I knew I could start buying next size up (and told family and friend this as well). You'll never have enough vests and socks tho!
I recorded lots of his fave TV shows.
I also stock piled some of my own toiletries and laundry detergent so that I had plenty waiting for when I went onto stat pay. Also this helped in the early weeks when I didn't know what day of the week it was let alone what I had actually gone to tescos for 
Start prepping your list for foster carer about routines etc...grill them about everything from the second DC wake until bed.
Prep some meals for yourself and freeze, intros are hard and exhausting as are the first few months weeks.
Find out what their fave foods are also.
Order your talking album now, they are forever selling out. I think Argos have some Lamaze ones at a good price.
Buggy and maybe one of those toddler step things that attach for the older one to stand on (can't think of the proper name).
God it's so exciting just thinking back to this stage has given me a little buzz, you must be on cloud nine!!!
Things I wished I'd done differently....not bought so many toys at the start! In our first 6 weeks my DC came home, had Xmas and a birthday....and of course everyone bought him coming home, Xmas and birthday prezzies, that on top of what I had bought the house was bursting, 6 months on I still have unopened prezzies in the cupboard.
I wish I had gotten rid of more stuff and cleared my wardrobe etc, you honestly need so much storage space.
Best of luck and keep us updated
