The following list is a basic check list of the core areas you will need to provide pieces for. You may, in some cases, get away with very simple solutions (e.g. fixed phone durations), or be able to borrow from other voices/languages, but whatever you end up doing, you will need to provide something for each part.
You will need to define
Token processing rules (numbers etc)
Prosodic phrasing method
Word pronunciation (lexicon and/or letter-to-sound rules)
Intonation (accents and F0 contour)