i suggest most of you should try writing most of your posts with the following format:
1-2 sections. (a quote and a reply is one section)
80-400 words per section.
quote at most the same amount as you write, plus 200 words. (not counting attributions. the number of people quoted should usually be kept to 3 or fewer, but sometimes more is ok.) try to think about quoting like you were writing a blog post and consider what quotes you would actually copy into it.
try not to quote partial thoughts from other people. as a loose guideline, a thought is typically around one medium sized paragraph. generally avoid breaking up their text mid sentence or mid paragraph. or if they write several short paragraphs that go together, leave them together. let them say their thought. then reply to the thought overall.
if you want to make a small detail point, you can break in in the middle of their thought. try to keep the break in on the shorter side, and only one break in per thought they have.
some people will take a thought i write and then break it up into 4 pieces and write a bunch of little detail replies. the forest gets lost for the trees. what i was saying gets lost, and the replies don't have a big picture to them.
if you have a lot to say about an email, reply multiple times.
if your thoughts are separate, they don't need to be in the same email. if they are related, but exceed 2 sections of 800 total words, then it's hard to put them together. you're now trying to write something a bit longer, and make it fit together. generally i recommend you don't try that. think about how to separate or shorten your points.
if you want to write something too short, like a one sentence question, or i "yes i agree, go on", then consider what you can add to make it better. replies like that are often boring to everyone except the one person you're replying to.
you can add some extra thoughts on the topic. you can add an explanation of why you're asking a question or why you agree. you can add some additional questions. you can add some clarification of what you agree with or what your question means. you can add an argument you think is true, or one you're unclear about. you can add a statement about why this topic is important and you want to discuss it. you can add a statement about why the audience should care and join in.
don't give up. think about the topic more and make your post better. getting up to 80 words for your section shouldn't be that hard. if you get really stuck, just write that you couldn't think of anything else to say, and maybe a guess at why or how you got stuck. ask for advice how to think of stuff to say, or examples of what you could have said, or whatever you think would be helpful.
also, if you have at least one meaty section of general interest, then having one (or even several) really short sections is way better than if they were the whole post.
FYI this post is around 500 words. 400 words is pretty long. most of you should usually end a section by 250 words.