Here are a few bits of information to provide a rough idea of how different houses and species tend to regard one another.
These are overly simplified and only generally true, and many exceptions exist. I invite you to stray from the stereotypes as much as you'd like, as this is usually where interesting things happen.
Cults will probably not be listed here as I intend on eventually having dozens.
In general, houses do not associate with those from their opposing house, and any camaraderie of this nature is usually frowned upon by higher ranking mages, if not grounds for expulsion.
Mages of Psilysium are generally welcoming of other houses' company, given they're not from Vorn; many joke this is because they're all high, but others see the house as particularly open-minded.
Those of Umbrasia tend to find the revelry of house Vorn to be abrasive, and see Vorn mages as gluttonous and materialistic.
Omnillian maintains a tenuous relationship with all other houses, and many Omnillian mages see the other houses as obsolete and a waste of energy. Mages of this house are known for being exceptionally intolerant of Morphoria mages, and some see fit to use them as experiment fodder. Likewise, one of house Morphoria would delight at any chance to turn a stuffy Omnillian mage into a lamp.
In general, independent cults are not particularly interested in the affairs of the official houses, and their regard for house mages varies. Cults may recruit more aggressively than houses, due to being smaller; any in the company of a cult mage is at risk of being pressured - if not threatened - into joining.
Lehlts get along with just about any species but their own, due to their need to be envied by others; another of their own kind in their midst would mean unnecessary competition. While many other species know the friendliness of a lehlt to be largely superficial, many don't tend to care, and welcome the company. One exception is slyne, whom some refuse to associate with for the fear of being seen as cruel.
Oggori don't often mingle with those of their own kind - or with lehlts - for similar reasons: most oggori would prefer to have the largest harem, and most aren't keen on sharing. That said, there are many exceptions, and many oggori aren't interested in this lifestyle at all.
Ravels, with their love of substances, are often drawn to oggori for the promise of venom. As many ravels are introspective and accepting of the city's darkness, they also tend to be welcoming of slyne.
Due to their diet, slyne tend to be regarded unfavorably by species who are morally preoccupied. Petrids tend to worry about the safety of others, and the guilt-ridden krudge is sometimes put off by any slyne who seem overly blithe about their circumstances.