Re: passportIf you apply for a new passport you are allowed to carry over the last nine months' validity so your new passport can be valid for up to ten years and nine months. If you're not planning to travel in the foreseeable future, why not just wait until nine months before your current passport expires to get the new one?
Re: passportExactly as Orangutan has said above and this is the Gov.UK link which explains changing your name back to your maiden name ...... you will need to click on section 4 for your position.
Re: passportYou say 'you've been told' about validity etc ... but by whom? Someone official, someone who should know or just someone? All sorts of people think they know all sort of things but unfortunately they are often mistaken