If you are getting a proper scratch post it needs to be at least 3ft tall and it needs to not move or wobble. Cats don't like **** that wobbles and unless the post is long enough for them to stretch on they are less likely to use it.
A great cheap litter is Chick Crumbs. Its simply the food that normally gets fed to chicks. When water touches it it bunches up and forms a ball so its really easy to scoop out and it also gets rid of the odour. A 20kg bags is about £8-9 and lasts us a month with 3 18 month old cats.
An enclosed litter tray is great, as no matter what litter you use they are going to try and get as much of it out of the tray as possible.
Try zooplus for your food and supplies. Also check out the petforums.co.uk site for some great info on food both wet and dry.
Take lots of pics when they are small as you'll regret it once they are bigger if you don't, they grow up too fast
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Just because the vet says they can now go outside doesn't mean you HAVE to let them outside. An adult cat has the intelligence comparable to a 3 year old so there is no harm in waiting a few extra months for the cat to wise up a bit before letting it out. The butter thing is an old wives tale. If I smear Marmite on my cats feet and it comes back at the end of the day does that mean it was the Marmite or the cat knowing where some food and a sofa was?
When you do decide to let it out don't force it out. Just open the door and sit outside and see what it does. The first time I opened the door for our three it took a full 5 minutes for the bravest one to go 4 feet from the door. Gradually ramp up the time they are out and give them a treat when they come back in.
Similarly, when you get it home don't pull it out of the carrier and effectively say "you live here now, like it". Open the carrier and just sit down and let it do what it wants to do. Typically it's going to be timid and a little disorientated but if it thinks it decided to come out and explore that's going to be better for it than being pulled out and plonked on the floor or your lap. Just as you need to get used to its particular ways, it needs to get used to you, your home, the smells, the furniture etc.
Get pet insurance. Ours is £6.70 a month per cat and while it doesn't cover the most severe scenarios it will cover things like getting run over, falling and breaking a leg, drugs for less exotic diseases etc.
One last thing and by far the most important.
get some of the same food that it has already been eating to feed it on when it first rocks up. Cats have sensitive stomachs and the stress of having a jab or de working (typical at that age) does not need to be compounded by giving it the ***** because you also changed its food.
When you do want to change its food do not just stop giving it the old and give it the new. Gradually introduce it over a week a bit at a time. If you don;t chances are you are going to have very wet poos!
We had cats when I was growing up living with my parents, but never had any since I left home so I'm keen to hear from all the kitteh owners here. 
............making a note of that.....
............Definitely getting a scratching post though. 
