A few more guidelines ...

• Latin masculine names are predominantly 2nd or 3rd declension (but there are a few exceptions that are 1st declension and they should end in -a).  Feminine names are generally 1st declension.
• Two major practices seem to be present in the formation of masculine names in Latin:
  • Either a name is Latinized into a standard 2nd declension form (e.g. Henricus, Iacobus, etc.), causing it to have the usual -us form in the nominative
  • Or else it keeps its usual form in the nominative case and is declined only in the other cases either following 2nd declension (e.g. Alexander, -dri) or, more often, the 3rd declension (e.g. Joannes, -is, or Leo, -nis, etc.).
• Names seem to usually only follow the first three declensions.