My younger brother was into club culture big time and was seemingly very happy too. He was (is) a very popular man. Then somehow he managed to get involved with a strict muslim girl. Well 15 years later they are very happy and have 2 children. She gives him shit all the time about religious stuff and he just don't give a fuck. He just loves her and not the religion. However the clubbing stopped and he does attend the big religious events just to keep the peace but he is not in anyway religious. I guess he made a personal compromise just to keep her happy. And she keeps him happy too in a home making kind of way.

I don't see religious views as a problem, but the degree to which someone might be committed to their religion.
And next, if they're not too gonzo - it's if we can respect the differences and decide to coexist peacefully. Kind of like any other significant differences !

I was married to a believer (rural Methodist background, college educated -- since deceased) when I deconverted. It was not in any way a problem. But our relationship was not based around church involvements and relationships, it was based around each other.

The extent to which this would be a problem (and it could be a HUGE one) would depend on the individuals involved. The more liberal the believer, the better your odds. I don't see any issues for example courting someone who goes to a Unitarian Universalist congregation, or something like Episcopalian, those folks hold their beliefs very loosely indeed. So long as you don't have an issue, your partner is not likely to. Open communication about expectations early on should clear up any concerns.

On the other hand if you marry someone who is a rabid fundamentalist, then it's a horse of a different color.

An interesting aspect of this is that there's no guarantee an atheist who marries another atheist wouldn't at some future time find their partner becomes a convert to some unsavory cult or other. And even my current wife, although an atheist, has some openness to religious-derived notions at times. There are no guarantees in life. You just don't want to front-load yourself with problems, and I'm suggesting that marrying a liberal believer shouldn't present any inherent difficulties unless one or both persons make an effort to blow it out of proportion. For example if you get the willies just thinking about marrying even the mildest of god-botherers, then by all means don't. But I think it might be needlessly self-limiting.

Very important, even just friends I have had in the past were just waiting for me to see the light.

Always does come up and they will not rest till you are unhappy sitting next to them in their church