About linking stuff, I think that might not be possible (for me at least). I'm not aware of the existence of in-depth discussions about religion on this series. The discussions I AM aware of deal exclusivelly with one portrayal of religion on Castlevania, which would be on the animated series, a product that mirrors very poorly what the actual games say about religion as an institution.
That said, I want to contribute a bit with some analysis done by me:
In this series, religion is portrayed in a good light, so much so that the lack of faith is a catalyst to Dracula's return. And this is because religion brings human union. The overall theme is "human bonding" and the games use religion as a symbol to embody this. I understand the difference between "religion" and "faith", but as a piece of media with certain restrictions regarding nuance, Castlevania doesn't quite have the luxury of separating both, so it conflates both concepts in favor of furthering the narrative it is trying to tell.
On the games' lore, when individuals get lax with their faith in good, Dracula's insidious influence isolates them from their peers and brainwashes them into evil. We see this repeat over and over with the cultists/vessels that revive him -- it's almost always a case of them getting distanced from others, of cutting away their connection to humanity and becoming alone, and this causing Dracula to fester on their minds. This trope of "being alone is bad for you" is a very ingrained theme on the series, and it started way back on the very first Castlevania: while the people are celebrating Easter -- a religious celebration that unites people -- cultists are far away, isolated, seeking Dracula's resurrection. On Castlevania II, Simon had no way of overcoming the curse if not through the collective (and admitedly cryptic) help of the villagers. On Castlevania III it took the power of four characters representing different aspects of humanity (and two of which being summoned by the Church on a holy war) to finally put down Count Dracula. So you see, this started early.
In this series, religion is used as a core aspect that brings people together and strengthens their bond against the influence of evil. When Dracula starts shit-talking religion and telling Richter that people submit to it over egoistic desires, Richter replies with (in Japanese):
"Mere power is not what leads mankind. Respect and generosity: That is what truly guides humanity!"Meaning that people don't seek religion to "have power over other people" such as Dracula seems to think and want to do, but instead to cherish on the bonding that it creates and the fruits of it, such as generosity. But, what happens when one uses such means to manipulate others? Well, the series shows you that they either weren't human in the first place (The "priest" Zead), or that they have already a strong, negative connection to Dracula (Barlowe, Graham Jones). The bottom line is: If you abuse the power used to bring union to instead control others, the essence of humanity is lost and this is not what humanity's relationship to religion is about.
And also, in this series, WHAT religion is important doesn't matter. To illustrate, here you have the Catholic church continuously trying to banish Dracula and employing people of otherwise pagan backgrounds to do so. The Church, here, is aware of the multitude of different religions having power over the forces of evil (the most screaming-obvious example being Juste Belmont using the powers of Hindu deities to subdue his enemies, or the Belnades contacting "spirits of the atmosphere" to employ elemental magic). Also on this series, persecution of pagan minorities such as witches is not something carried out by the Church, but instead by coaxing from the creatures of the night -- the Church was instead taking people like this under their wing and protecting them.
Another example of the "all religions are good/effective" theme in this series is how the ultimate defeat of Dracula is brought about: It's not Cristianity that defeats him, but instead Shintoism. A host of Shinto priests are brought to Romania, and through their customs and traditions (and trust me, this goes
really deep), they are able to seal Dracula's Castle inside an eclipse, ending Dracula's resurrection and achieving a feat unattained by the Church for 500+ years.
And that is not getting to the Buddhist symbolism and how it potentially affects Castlevania's "cosmology", if we can call it that.
I wrote more extensively about it over here, but we can just cut to the chase and see that, in the cv universe, there exists reincarnation, something that exists on some religions but not on others (such as Christianity).
So, if you write about this, this is what I can contribute at the moment. On Castlevania, religion is a core trait of humanity in that it's like a weapon that humans have built to fight back the darkness. Though there are some favorites (Belmonts are so Catholic they wield
frikkin' Jesus himself as a goddamn weapon), it doesn't exactly matter which religion. It only matters that, as a weapon of humanity, it works by uniting the people and not letting them be alone.