Considering ancient civilizations, like egyptians and mesopotamics, several gods would be very nice to have, giving you the possibility of multiple choices of buffs. Like mesopotamics, the city would have a major deity for it (either working on protecting the city or handing bonuses for something), and villagers would be able to hand out crops and/or sacrifices to appease these gods.
One way, in my imagination to balance this would be first creating two types of god “pantheons”, either politheistic or monotheistic gods. The first would allow the city to choose from a preset quantity of gods one to be its patron god, and handing out to the city what I would call “Major buff”. Say Sayrna (???), the goddess of harvest. She will hand two abilities, one passive (a straight 15% increase in crops output) and an active (a small rain formation on the crops you are planting), which would require a dedicated temple to herself (say a 10 x 10 square temple, with 5 people working as priests). These people would serve as the link between gods and people, managing sacrifices and crops directed to the gods, which would increase it’s ability bar % until it hits 100% and allows you to use your ability.
That would also mean that you would be able to build other temples for other gods as well, but since these aren’t the patron gods protecting your city, their role would be much smaller (For instance, Ronjar, God of Forging (???) would grant only a 5% passive buff to forge production) and would require a separate temple for it as well (much smaller, 4x4 with 1 priest to it. This way, players who prefer to micromanage and give some more direction for their cities could do so via religious means (though religion alone would not save a city from bad management).
Also we must consider the following: As ancient civilization worshipped gods that we’re much more like humans (betraying each other, loving, taking revenge, etc), if you decided to change your patron god, by destroying your patron god’s temple, something bad would happen to your city (a years bad crop season for instance). The idea here is to actually have consequences that affect your city in case you decide to play with the deities for your own favour. This should a careful plan and should be though well before changing your patron god.
Examples of politheistic gods:
Zareus - God of Lightning and leader of the Pantheon
Passive: 15% towards magical effects of caster units, being those magics for protecting, attacks or buffs, 5% for being a smaller deity
Active: 1 Bolt of lightning that deals X damage to a target creature (Yes, I’m thinking also against world bosses).
Leaving its patronage: 3 buildings will be struck by lightning at random at your city, causing fires.
Sayrna - Goddess of Harvest and fertility
Passive: 15% bonus towards crop harvesting, 5% for being a smaller deity
Active: A 10x10 rain cloud which accelerates the crop growth by x%.
Leaving its patronage: Bad crops yield for the whole year.
Ronjar, God of World Creation and Forging
Passive: 15% bonus towards material forging (this could be from iron into iron ingots and iron ingots into armor/weapons), 5% for being a smaller deity
Active: Grants the Ronjar’s Creativity to one smithy, allowing him to produce top quality armour/weapons for x months. (or days, whatever balances better out).
Leaving its patronage: He’ll summon a mountain in the middle of your city (5x5), which would destroy a few buildings, but it is gatherable (or not, if you like the “gods punishment thing” to be a token of you city).
Demares, God of War and Violence
Passive: 15% bonus towards combat units, increasing their damage output, 5% for being a smaller deity
Active: Grants Demares’ might to one combat unit, creating an avatar of demares, which would deal extra damage and have extra health, plus more bonus mitigation. Would be usable for only one combat.
Leaving its patronage: Violence would errupt in your city, making some villagers mad with rage, becoming violent and therefore, to be put down by combat units.
Haderon, Lord of the Dead and the Underrealm (would need a cemitery structure)
Passive: 15% increased life span of the living units (considering they eventually die of old age) and 15% extra health to combat units., 5% for being a smaller deity
Active: Allows for Haderon’s Embrace: Engulfs one unit and pulls it towards the underrealm, eliminating it completely (unusable on World Bosses). No EXP is awarded this way.
Leaving its Patronage: Your dead rise to take Haderon’s revenge upon your city! 5~10 skeletal/zombie warrior appears in your city.
Zitonia, Goddes of Science and Knowledge
Passive: 15% increase in research (considering there’ll be research to be done), 5% for being a smaller deity
Active: Granting the Zitonian’s Knowledge, allows one scientist for a double the amount of research grant towards a technology for x months (or days).
Leaving the Pantheon: The city loses some of its scientists to the great zitonian library of olympican research.
As seen in the examples, having only one god patron would give a huge bonus, but trying to have ALL six gods in your city is a little more difficult. The idea here is to make the choice between having an active deity ability or not, which would be the monitheistic approach.
The idea around monotheistic religions in our world is that this monotheistic god resembles WAY much less humans and has achieving some sort of perfect state, which makes it less like humans, and therefore, much more distant to us. He’s perfect in every aspect (I’m an atheist, but I’m explaining this though a historical point of view - See Peter Berger), and being so distant to all humans makes for VERY LITTLE interference in our daily lives (“We will save ourselves”).
While the politheistic approach does sound rewarding, the monotheistic approach has its own perks. First of all, since this god is all perfect, ALL aspects of life (Magic, Farming, Crafting, combat, science) gain up a straight 10% bonus from this god. He also doesn’t require more then 1 single temple in your city (which could also vary in size), but as a con, he wouldn’t grant ANY sort of active ability for the player. But if you decided to go for the politheistic approach later on, or, even the atheist approach, nothing bad would happen ("the judgement comes in the afterlife, not here), and more could be saved to the next winter (since no crops nor sacrifices would be needed, just belief).
These are the aspects I think would appeal much more to a city, on a religious point of view. We see older civilizations and become intriged on how they interacted with their gods and how it influenced in their daily lives. If this could be achieved in Stonehearth, a new depth layer could be established and some interesting ideas would come out.
My thoughts on this, and sorry for some bad grammar.