Hello, I play Bakar i Erigo, Freeborn Winter ritualist and hakima. Other people have done an excellent job of giving you general answers, so I’ll swing in with some Brass Coast specifics.
While a mana site is the default option for someone playing a magician, another option that is quite popular for magicians in the Brass Coast is a fleet. You can send off a fleet to trade with 1 of 9 foreign ports between events. There are currently 3 options that provide mana crystals (among other resources), though not as many as a mana site would. The other benefits of a fleet are that they can be more interesting to roleplay around (yay boats!), particularly given that in the last year or so there have been many special opportunities for fleet owners to take part in special projects like mapping areas of coast, attacking enemy ports, or rescuing the Zemress islanders. Fleets also provide Freeborn votes for a handful of Imperial titles in the Brass Coast.
There is a page about magical traditions in the Brass coast that I’d recommend you read, as it gives you a rough idea of how to put a Freeborn flavour into your magical roleplay. One key line of interest referring to family mages (magicians who choose to use their magic primarily to serve their own family rather than the whole nation as hakima do) states that “These magicians tend to be practical, and often combine their study of magic with crafting or medicinal lore.”, which could be of interest if you want to go down the magician + hospital route. You would be spreading your xp rather thin if you went for physick skills, Night lore, and Winter lore, but it is certainly possible. If you want to lean more heavily into magic then you could just pick chirurgeon rather than physick to leave more points free for picking magical skills.
You might also be interested in the hakima page, which goes into detail about one kind of archetypal Freeborn magician. It’s a very good page, but I’m biased because it has my face in it.
As far as groups go I do not know of any specific Night covens in the nation, though there is a small smattering of Night mages mixed in with covens of other realms amongst the family groups. I’m fairly certain there are currently NO Night hakima that regularly attend events, so there is an opportunity to fill a gap if that is what you’re looking for. If you are interested in Winter and being a hakima (or perhaps becoming one in play) feel free to get in touch.