Hi dreamrthts,
Custom Document Properties can be created along the lines you suggest - assign a name, then populate the named property with a string (eg Name: Prop1; String: "The quick brown fox jups over the lazy dog."). The simplest way (IMHO) to insert the string associated with this Custom Document Property into the document is to select the point where the string is to appear, press Ctrl-F9 to create a pair of field braces (ie '{}'), then type 'DOCPROPERTY Prop1' between the field braces (ie '{DOCPROPERTY Prop1}'), then press F9. If you want to change the displayed result, wherever it appears in the document, simply change the property's string, then select the whole document (Ctrl-A) then press F9 to update the fields.
As for the formatting issue, the whole field can only have one format - usually that of the underlying paragraph Style, though you can add a Charformat switch to the field so that a different format can be used.