1) Buy the Haynes manuals for it... there's 2 of them, the regular one and the restoration one. http://astore.amazon.co.uk/jdcouk-books-21?_encoding=UTF8&node=28
2) Bookmark http://www.minisport.com/ 'cos they have loads of bits for Mini's (both classic and the bmw thing).
3) Get "Mini World" magazine from your friendly local newsagent http://www.miniworld.co.uk/
4) Get books on Advanced Driving, such as "Roadcraft", "Advanced Driving: How to further Skill & enjoyment in Motoring" + "Paul Ripley's Expert Driving" for tips on driving it more sympathetically and keeping out of situations that won't do the car much good.
http://astore.amazon.co.uk/alltheinterweb_books-21/detail/0117021687 http://astore.amazon.co.uk/alltheinterweb_books-21/detail/085733221X http://astore.amazon.co.uk/alltheinterweb_books-21/detail/0716030098
5) Make sure the wheelarches are properly sorted out to avoid rust... some people insist on giving them a good coating of Hammerite, then sealing it with Waxoyl.... and when using it at this time of year when the councils have been gritting the roads, hose off the underneath of the car with one of them Pressure washers at the end of the day to remove the salt. With the body, it's mostly developping an OCD keeping track of scratches and stonechips, and fixing them on sight.