I'm not sure about in Scotland, but in the USA and Canada, it is pretty standard to get your cats fixed. Where I live, you get a small discount for having a multi-pet household. You're best bet is to call around to vets in your area.
I am really a believer in spaying/neutering. I know it is kind of sad to think of no more babies, but your going to have a full house as it is! 6 cats, Wow! There are also so many unwanted kittens in this world. I'm sure that you would find good homes for them, but that means that OTHER kittens are NOT getting good homes. Another reason it is so important to fix your cats is because they are way less likely to get mammary cancer and of course, reproductive cancers. Female cats in heat will find a way to get outside, no matter how hard you try. Male cats will spray, fight and roam further from home. It really is for the best to get your kitties fixed!
As for the operation, the female cat is put under a general anesthetic and is placed on the operating table on her back. A small incision is made in the lower abdomen and the uterus is pulled to the opening in the abdomen. Then the horns of the uterus are clamped (there are two) and so is the end of the uterus (at the top of the vagina). The uterus is then removed and everything put back in place. Then the kitty is stiched up again. It is a very simple operation and does not take long at all. Most cats are back to themselves within a few days.