I'll try an answer you questions, Stu, but in a different order than you asked them, because I find that easier!


I'm not sure the analogy with football teams etc is valid though; these are opinions and not beliefs, not the basis for forming a moral code, for example

OK, they aren't a perfect analogy - nothing is, so let's take a moral code example. You and a friend, A.N.Other, are considering whether the UK politician's second homes dealings were immoral, and you both agree that theft in general is wrong, but that laws in general should be obeyed. Let's suppose you feel that the case is so obviously theft that it is immoral despite being legal,while A.N. insists because it is legal it is moral. You are convinced you are right but if you are fair you can't really say A.N. is wrong, just that he weights the parts differently to you, and that he is entitled to that stance as you are to yours.

Does admitting you might be wrong in your belief in a deity not mean you have a smidgeon of doubt about the existence of that deity?
There are at least three levels to that one.
a) The absolute case: "there is no God". Yes, sometimes. Not very often, but it happens. Dylan Thomas wrote "No man believes who cries not 'God is Not!' and there's something in that. One way of getting a deeper understanding of anything involves running into brick walls occasionally ...
b) The philosophical case: "What we cannot speak about we must pass over in silence." One problem with the word 'God' is that it means so many different things to different people. It is very likely if any two people start talking about 'God' they have quite significant differences in understanding. One of the things that people (largely) agree about God, is that his existence (if any) transcends our ordinary experience. Which makes describing it/him in ordinary words that are non-transcendent almost, or entirely, impossible. Tough one that. And in that sense, I reckon it is extremely likely I do not believe in what you mean by the term.
c) Personal interpretation. My understanding of God is always limited, and always partial. That means at times I can see God as fully embodied in a few mathematical equations, at others shown through nature, at others more like human emotions. All are right, all are wrong, all are incomplete. And in this final sense I'd say I 'disbelieve' in God (in some senses), and 'believe' in God (in other senses) in a way that changes hour by hour.   

If it does, how do you address that doubt? Reflection? Scripture?
Primarily reflection. Pete fired a shot at Christians who aren't fundamentally driven by Scripture. I take the hit: I see it more as exemplars than rules. The one bit I take absolutely solidly is common to most religions and usually referred as "The Golden Rule": it's the one about treating others as you would want them to treat you. All the rest, roughly, is examples of that rule in action in particular situations. But the situation you find yourself in today with certain people doing specific things probably doesn't correspond exactly to anything written. So you have to use your intellect and understanding to come up what seems right. (Which is one of the reasons when people talk about pick-and-mix Christians because they seem to choose some bits of the Bible and not others, it brings a wry smile)