I haven't looked this up 'cos I know I'd stumble across too many unwanted spoilers if I did.

At the moment I'm level 51 and I've just got the quest to find the Elder Scroll. But I haven't decided what to do about imperial/stormcloak conflict yet and I haven't done much at all for any of the Jarls outside of Whiterun. Having talked to people a bit in Winterhold much earlier I realised I was going to get svcked into this without understanding enough to make a decision and backed out of it. I think I'd like to settle this issue before continuing with the main quest line.

As I say I'm not looking for any spoilers but I'd like some advice on how I might approach obtaining information (in game) about the relative merits of each side's position and the likely consequences for the world of electing to support one side or the other (on the assumption my intervention would tip the balance one way or the other).

They both have their respective merits and there is no clear definition as to who joins which. It depends on how you personally perceive the situation. Both have good sides and both have bad sides just like there are good reasons to join one and just as good reasons to join the other.

This is gonna end well !!

You don't have to do anything with the Civil War in order to complete the Main Quest.

Indeed, by not touching the Civil War, you actually GAIN a quest to the Main storyline that is well worth it. So I say don't worry about the War, and carry on. If you don't know which side to support, then don't bother with that story arc. The War is a static affair - beyond said quest, it has zero relevance to the fight against Alduin.

For information: talk to people you meet. Read in-game books (but be aware that some, like the infamous The Bear of Markarth are heavily biased one way or the other). This goes for people you talk to as well. Use your eyes and look around you. Are the things you hear consistent with what you actually see? Might some people have ulterior motives with supporting one side or the other? Might there be other explanations for certain behaviors?

Or you can just follow your (or your character's) heart. Neither side is completely "good" or "bad".

As for consequences, the main thing is that jarls will be replaced with persons supporting the winning side. The rewards are the same for you, and the quests are basically the same, but with different targets.