can we have a couple more of these buildings?
The Kaaba and the Ganges banks in Varanasi come to mind
Not really. I'm not a fan of overloading the mod with superfluous wonders. The requirement of St. Peter's Basilica is meant to reflect how the Apostolic Palace worked in CIV (it would be the Apostolic Palace again, but St. Peter's already had art). The Papacy is the most advanced of the five religious institutions, so I think it best that the Papacy have the additional requirement of this wonder.
On that note, five religious institutions have been settled on:
The Papacy - The Papacy is an institution focused on diplomacy, and on controlling or influencing civilisations that share your State Religion. Within the Papacy is the Curia, of which all civilisations following the State Religion of the founder are members. The founder of the Papacy automatically begins as the Papal Controller. They lose this status once their Piety level reaches neutral (you lose additional piety for being controller). When this occurs, the civ with the highest faith output becomes the next controller, is given free piety, and the counter begins again. When Papal Controller, you may enact decisions that affect all members of the Curia - this includes calling Crusades against heathen civilisations, excommunicating members, or setting certain rules against them (for instance, deciding on Papal Investiture for extra faith for all members or Free Investiture for extra gold for all members - the Papal Controller getting a larger benefit, of course). When the player is subject to an AI Papal Controller, this will present them with unique events, as well as the unique "Request Indulgences" decision. If you're not happy with the way you're being treated by the Papacy - you can change your State Religion to leave (if you have high enough piety). Finally, it is important that the Curia remain pious - so as Papal Controller, you'll want to occasionally give out indulgences. This is because, for every member of the Curia with a piety level of neutral or below, there is an increased chance of a Reformation event occurring, which will cause a new religion to be founded in the capital of one of your impious members.
The Mandate of Heaven - The Mandate of Heaven is a high reward, high risk institution. Whilst piety is high with the Mandate of Heaven, you are in a perpetual golden age. But, whilst it is low, there is a chance of anarchy. Whilst you will be given a unique Mandate of Heaven decision, and unique events to go along with it, to improve your piety, you will also lose piety faster depending upon how much unhappiness and happiness you have. Finally, the Mandate of Heaven can be claimed by any civilisation that happens to conquer the capital current claimant.
The Caliphate - The Caliphate is an institution that requires a bit of micro-management to get the most out of it. Those familiar with CKII will know of the decadence system for Muslims. The Caliphate will work similarly: low piety will afford scientific bonuses, whilst high piety will afford militaristic bonuses. However, these bonuses will be dependent upon the number of religious followers in your empire. Where the Caliphate will gain its own unique decisions and events, it will lose additional piety for every city following the Caliphate's State Religion not under the player's control; so the Caliphate must be a continuous empire. The owner of the holy city for the State Religion will assume the Caliphate if the previous Caliphate has been completely eliminated from the game.
The Patriarchate - The Patriarchate is a shared institution - where all members of the same State Religion share equal - defensive - benefits. No further details at this time.
Imperial Cult - The Imperial Cult is a local institution - any civilisation (so long as they haven't founded one of the previous four institutions) can create an Imperial Cult, which focuses on production and food related improvements. However, the more Imperial Cults there are in the world, the faster piety will degrade. Of course, unique decisions and events will be available to aide in counteracting this degradation. No further details at this time.
All of these institutions can only be suspended after adopting an ideology, after enacting the appropriate decision (Secularise the State for Freedom, Endorse State Atheism for Order, and Create a Personality Cult for Autocracy) - so the decision to found one should not be taken lightly. They will, however, hopefully, add a bit more variety to your games (and hopefully the Papacy will be both an interference and a tool in your empire building).
Can you elaborate on how you've done away with the Pantheon race? Did you simply fix the faith required to 10, or did you do something different?
You mention religious resources, what are they?
Yes, I've merely fixed the faith required for a pantheon to 15.
The religious resources are Lotus, Saffron and Obsidian. These are special resources that have a natural faith yield.