Technically speaking the bold, italic and bold-italic variants are distinct "fonts", so that alone explains the usage of "kpfonts", plural. In its case, the old style numerals version is actually technically a distinct font, and with kpfonts, there is also a "light text" variant, which is also a completely different font. (See its documentation.) And if that's not enough to convince you, kpfonts also has its own complete sans serif and typewriter fronts for \textsf and \texttt and so on. So the plural is definitely appropriate.
Apart from it, I'm not sure which fonts support the Old Style ligatures, such as ct, sp, st, etc. The only ones that come to mind are the ADF fonts such as
baskervaldadf,
romandeadf, and
electrumadf. (In the case of electrumadf, this is just perfectly silly, since I cannot imagine anyone using that font to typeset a document where historic ligatures would be appropriate!) I like Baskervald though -- it may be one to consider.
The OpenType versions of Linux Libertine (which is farily similar to Venturis) definitely have those historic ligatures too.
See the project page here. but I don't know of the Type1 variants for the
libertine package have them -- or if they do, I don't know how to access them offhand. However, you could definitely get them if you used XeLaTeX rather than pdfLaTeX with the
fontspec package. Of course, if you go that way, it makes the possibilities wide open, since you could use any commercial/professional font with these characters.