You may find that getting a bed for the cat to sleep in is a bit of a waste of money - so if you haven't already shopped don't spring for anything expensive, if at all. I've had 6 cats in my lifetime and none of them have ever slept in cat beds purchased for them - in a cupboard, under a table, on the chair my DH likes to sit on yes, in their own bed or basket - not a chance!
As for cat carriers, you can probably pick up a small sturdy plastic one from somewhere like Pets at Home for about ten or fifteen quid.
You'll probably need 3 bowls - one for water (never cows milk, as a lot of cats are actually lactose intolerent) another for wet food and another for dry food. My cats have water and dry food always available, and they get wet food 4 times a day.
I wouldn't worry overmuch about leaving the kitty by herself. Cats are pretty big sleepers, getting as much as 14-16 hours a day and she will quite possibly snooze much of the day away if there is nothing interesting to stay awake for. Just be sure to play with her in the evenings and she'll be happy.
As other posters have said, definitely don't switch the brand of food she is eating, cats can get very set on what they eat and are known for being picky. If you give her something different to what she is used to she may either just refuse it, or eat and get an upset tummy.
Finding a good local vet is worth doing right away - make sure the kitty is healthy and has no problems.
Worming is usually done by pill (though you can get liquid forms) you can buy worm pills in pet stores or online, or visit the vet and have them drop the pill in for you (but they will of course charge you for that.) It all depends what the cat is like and what your budget is. I have one cat who is very placid and easily 'pilled' and another who turns into a flailing howling psycho and requires both me and DH to manage her - and even then it takes a few attempts and we both inevitably end up clawed and bloodied. We repeat this madness every 3-4 months.
Fleas will probably only be a problem if it is an 'outdoor' cat. I swear by Program for my cats (six-monthly injections at the vet) and never have flea issues, but I know a lot of people do well with monthly drops on the back of the neck like Frontline or Advantage. Flea collars are okay, and better than nothing for an adult cat, but are not suitable for a kitten. Flea powders are a waste of time in my opinion and will make the cat hate you.
Make sure the kitten is kept indoors for a minimum of a week - preferably two - before you let it go outside. Cats are slippery and master escapologists, so you'll have to take some care about opening outer doors. If the kitten leaves the house before it understands that your house is her new home she may run away and not return.
The main reason I have two cats is so that they are company for each other, but they are both from the same litter and have always been together - introducing two strange cats can be risky as they may not get on at all.
I'm not sure what age your children are, but if they are young 'uns make sure they let kitty find her feet in her own time (even if she mainly hides under the bed for the first day or so) and don't drag her out to try and play.
Cats have to trust their owners and if their first impression of their new home is loud lively children trying to force them play they may be reluctant to ever join the family and you'll be stuck with a scared kitty hiding away somewhere.
And that was probably far too much info in one big lump hehe