Problem with the Open Exoplanets Catalog is that it does not supply enough of the parameters to model the orbit orientation. Of the three orbital Euler angles ω (argument of periastron), i (inclination) and Ω (longitude of node), it only provides the inclination. At a minimum I'd want the data source to supply both i and ω: the value of Ω is not known in the large majority of cases so you can probably get away with not having it (it represents the rotation around the line-of-sight, which most detection methods are not sensitive towards, though in some cases
relative values are known between planets in the same system due to dynamics, etc.). This is a pity because the Open Exoplanets Catalog is the only exoplanet catalogue I am aware of that also includes information about binary/multiple host star systems.
Of the various exoplanet catalogues, the ones I'd consider most suitable for doing a Celestia files conversion on are the
NASA Exoplanet Archive (no Ω but has a nice API), and the
Exoplanet Orbit Database. The
Extrasolar Planets Encyclopaedia may also work but I've noticed some rather questionable decisions taken in what to include in the data.