We have 2 maine coons and they are an absolute delight. Affectionate, gentle giants. They are just gorgeous. We have 2 moggies that I love to bit she too, but the Maine coons are just big hunks if gorgeous fluff. I'll attach a picture of my two for you.
Please don't get any cat from Gumtree. Ever. I have seen so many cats labelled as "Maine coons" just because they're a bit fluffy. Same with tabby cats being "bengals".
No reputable breeders use it. Go to the Maine Coon Cat Club website, click available kittens, and even then double check the breeder name on the GCCF website.
I've heard of a lot of breeders and am in contact with a lot of Maine Coon owners on Facebook - if you find a breeder name feel free to PM me and I'll do some digging for you.
Expect to pay £400-500 and be asked to sign to say you won't breed from them. Ask about mother/father (you should be able to meet the mother cat).
Ask about HCM testing - it's a genetic heart condition and the parents should have been DNA tested.
Other than that, expect the visit to go both ways - my breeder has turned people down before for not having appropriate provision or having a funny feeling about them! They will ask you as many questions as you ask them, if they are good breeders. You will also be able to tell a lot just from visiting and seeing the cats.
Hope that helps - feel free to PM any questions.
Rag dolls I can't help you with!!