When making a classic serif typeface, you need to do plenty of research to make sure it's going to be unique enough to stand out against existing designs. Likewise, if you're planning to do what amounts to a redesign of an old historical typeface (which might not exist as a digital font), you need to study it carefully and check a number of sources to make sure that there's a place in the market for it. Useful places to do your research are on the internet, in libraries and, of course, in printed specimen books.
Check out The Elements of Typographic Styles by Robert Bringhurst, The Encyclopedia of Typefaces by Jaspert, Berry & Johnson and A Book of Type and Design by Oldrich Hlavsa. Identifont is also worth visitiing.
Once you've got a design in place for the regular version of your typeface, you need to create enough weights to give the family a solid and useful foundation for the end users. The recommended basic package should consist of at least regular, italic, bold and small caps versions. It's even better if you can add some extra weights and a set of ornaments.
The following tutorial will guide you through the steps needed to create an original, yet classic, font and make it into a full digital working family.