Claire, some UK publishers prefer a serial comma (sometimes referred to as the 'Oxford comma') and others don't. Others still are happy to follow the author's preference, so long as it is consistent throughout the book or article.
The same applies to -ise/-ize, though -ize is becoming more common. There are some words that always use -ise, but I think the only word that always uses -ize is 'galvanize' (but I could be wrong about that). Beware of 'analyse' and 'paralyse', which are always 's' in UK English but can have a 'z' in American.
On hyphens the rule is to be consistent, but watch out for ambiguity: 'recreation' and 're-creation', or 'the dark-blue sea' and the dark, blue sea'.
On which or that, the presence or absence of a comma is the important thing: there is a difference between 'government officials who are corrupt ... ' = just the corrupt ones, and 'government officials, who are corrupt ...' = they are all corrupt. The same rule applies to which/that, who, and when, but usually you would use 'which' after a comma and 'that' when there is no comma, as in 'the wind that shakes the barley'.
On quotation marks and punctuation, US practice is easier - all commas and full points go inside; in the UK they go inside only if what is inside the quotation marks is a proper sentence starting with a capital letter.
I hope that helps and isn't too confusing.