I'm just writing my latest query too. It seems like a minefield. I have learned something though, through writing my query for my previous novel, which I didn't end up going forward with. You are probably fine if you get all the basics and the whole thing comes across well (the order is often a matter of preference, so it doesn't matter too much as long as it works, an agent won't turn you down for that -- although it seems sensible to me, after an introductory paragraph possibly with a strap-line, to get straight to your story before the agent losses interest). I've found that many people, including experts, have differing opinions on what is a good query and it made me realise that there may be no one truly right way, but get your plot across with no waffle and that helps.
Concerning feedback, it can be so useful, but where it comes in really handy is when you get a lot of (respectful) comments, then identify the points that a number of people are raising and you probably have something to work on, otherwise how are you to know if the advice is opinion or personal preference?
I've found The Shit No One Tells You About Writing podcast really helpful as every week the presenter and two agents examine three query letters (and some opening pages) and talk about what works and what doesn't. After listening to all the back issues, I'd soon listened to probably fifty query letters and comments.
From that podcast the opinion seems to be that queries should be 300 to 500 words long -- but as long as it takes to transfer your novel into a query concisely. Also, if you have a great strap-line, it's worth using it, as agents will use this with publishers and throughout the whole process. However, some books just don't transfer well to a strap-line (perhaps some literary books) so then it might not be such a good idea, although it's still necessary to nail your story in a couple of paragraphs.