@tanguatlay,
tanguatlay wrote:1. Should there be a comma after sentence?
2. Should the full stop be outside instead of inside the inverted commas (in British English)?
1. These are equally correct after the word 'sentence':
A comma
A colon
Nothing
2. Opinions differ between British style guides, but widespread practice in the UK is to place the full stop inside the quotes for a complete quoted sentence; otherwise the full stop comes outside. Thus in this case, place it inside the quotes.