Characters can be created using anything within the three WotC publications about character creation, the PHB, Element evil and the SCAG.
Starting characters will be level 3 with one uncommon wondrous item within the DMG or if you wish to create one confer with the DM that does not relate to their combat statistics.
The characters will have all of the languages they usually have along with one of the options of their cities languages.
Characters of divine nature may gain ‘Piety’ by following their dietys wishes and respecting the traditions of their god but by going against their god that can fall from their gods good graces.(DMG 22 RENOWN AND PIETY)
Characters of a martial nature may gain ‘Prowess’ (renown, strictly in the martial groups or armies)(They must choose the group specifically that they wish to join, joining the army may require them joining their squad in times of need to defend the interests of the city)(This includes rogue groups although this campaign will likely err on the side of neutral good and this is not recommended).
Characters of an arcane nature may gain ‘Quirks’ (renown strictly relating to the arcane arts and the groups there of) They may add a circle to their personal ‘Sigil’ (Which each magician has as of their initiation into the arts)(strictly based upon their school of magic).(SCAG 141 MAGE SIGILS)
After these things are noted on the character sheet i’d like for the characters to create a link that they have to another character, perhaps they know, perhaps they don’t. If its something far too complex about the character that you’re linked to for them to not know, the DM will confer with the character on your behalf.