Glad to see that you're having NFRS rats :) Our two big boys are from Rivendell in Kent, our two younger girls and baby boy are from Fugly/Seagull Stud in Brighton. All of them are gorgeous and so lovely :)
If you are anywhere near Brighton, the Fugly owner has a shop and sells things at internet prices or cheaper 99% of the time, and her hammocks are ridiculously cheap and well made. She's also extremely knowledgeable about rats.
Have a google of homemade toys for rats and also ferrets, tonnes of good ideas that you can get your kids on. It's second nature for us now to keep boxes and cardboard and scraps of fabric. We also buy kids jeans when they're on offer in cheapy shops or charity shops as they make great fabric tunnels! our old jeans get cut up as well.
Never underestimate how many hammocks you'll need. Some rats are big chewers and will go through tonnes. Our girls shred them, our boys are usually reserved!
If you haven't already, find a vet now who has a rodentologist or experience with rats. Don't feel funny about asking them questions, when things get bad for rats, they go downhill very fast, you do not want to be scrabbling around trying to find a vet who can actually treat them well in that scenario. A lot of standard vets are quite ignorant about rats, they last one I saw told me that I should put down my baby who had had some seizures, it's treatable, she just didn't know much about it.
Have a google for sounds rats make when they have respiratory illness. Rats are almost silent, so wheezing should always be checked out. They're prone to respiratory issues and if you can 'diagnose' it before it gets bad, you'll be better off for it :)
ratguide.com/ is a good website for general ailments. There are photos of conditions on there, but if you're worried about anything you can find out what likely treatment would be if you took them to a vet, how to care for them at home if they don't need vet treatment but need some R&R, etc.
The main other thing I'd say is to buy a large hamster cage, online (much cheaper), no more than 50cm high and not too big that you can't fit it somewhere. Rats can have accidents and may need a hospital cage at some point. We're unlucky and ours is out more often than not it seems 
One of our girls injured herself repeatedly and in a four week period spent about five days in her actual cage!
We have a tiny cage as well that we use to take them to the vet or to go to local rat events. Slightly bigger than a carrier so can fit three in at once without squishing them in! 