First time DM, excited but really trying not to mess things up so I'm probably overthinking things. I'm starting up a module I made for my friends and right now they've begun pitching characters to me (even though we're a few months out from playing and I'm planning, we all tend to get really excited too quickly). The one wants to play a LE cleric, Order domain which is totally fine but I'm questioning his exact relationship with his God. Basically said PC was born into being a leader of an organization that follows a specific god, who he's looking at Bane right now. Great that's fine and adds some interesting flavor to being a cleric. Only problem is the relationship he wants is less like somebody who worships and serves Bane but moreso just he wants the power and begrudgingly goes along with whatever he's told to do simply to have the power. Also he left previously mentioned organization that worships the god via uprising against him. This to me just seems like it borders on the line of cleric and something more like a warlock and he even said that RP wise it's more like a warlock with cleric powers. And at the moment I'm not sure on what exact spells and such he has in mind but he's going for a very supportive kind of build which is why he's cleric and not warlock. I asked if his character would be willing to follow everything the god says and he said yes because he's selfish and wants the power which I guess can work but it just doesn't sit well with me.

We're both willing to work on it since it's basically just conceptual phase but he's quite dead set on being a cleric. The other players have already picked their classes as well and they're all coordinating a bit to cover the general bases. I don't even know how much this'll come into play since I'm estimating the module to only take 8-10 or so sessions but I'd rather be safe than sorry, especially if I decide to continue building the world into an actual campaign. So, my options as I see them now are a) I let him play the cleric with the relationship as he wants, it's just a "reflavored" cleric so to speak, b) I try to work with him to make the PC-God relationship seem less like a warlock and more like a cleric, c) I have no idea I just know there's more options I'm not thinking of.

I’d suggest reading the description of a Cleric. It’s pretty clear that clerics are servants and divine agents. In the spellcasting part it says that the power of cleric’s spells comes from their devotion. He’s trying to completely change the concept and I’d suggest that you have him change his concept to be much more in line with the divine servant part. Warlock’s can struggle against their patron’s wishes, and frequently do, but clerics can’t by definition.

I personally would just let the guy make a cleric however he likes. As long as his personality and character fits the *party*, I don't see how making him have whatever relationship he wants with his Cleric's god is a problem.

I'd be more concerned that the "E" in "LE" is going to make him not a good team player with the party.  But if that's not a worry, why bother policing his character backstory?

Since this player is making an RP choice and not trying to outperform Clerics of his usual level, it's a little hard to deny him this unless you have a pretty specific idea of how the pantheon works in your world and you feel like his mercenary approach to faith is somehow breaking the mystical laws of that world.  Actually, I think the fact that he is choosing to play his character as LE and is choosing a god characterized by many as Evil fits quite well.  

One way to handle this 'powerhungry' over devout look could be that it is sufficient at low levels.  But as you level, the gods only reward higher magics to those who are truly devout to the diety.  This could be used as a roleplay incentive to show this progression from just a dark-hearted individual who simply sees the role in the church azs a grab for power to someone who eventually gets drawn into the fanaticsm of worshiping the diety.