Gavin,
No marriage for Richard Peters and Mary shows up in the Sussex Marriage Index at that time. You will need to widen your search to parishes outside Sussex.
Until you find their marriage, it would be unwise to link the other Peters records to them. Richard could be the one baptised in 1666, but you need something else, like a will or a property record to tie the two together.
You could check the catalogue database at
http://www.a2a.org.ukfor any entries of Peters in Balcombe in the West Sussex Record Office catalogues. You cannot view the records online, but there is usually a pretty good description of what the documents contain.
Good luck
Nell