There can be no doubt that writing content is the most important thing a site owner needs to do. If you have great content on your site you can get away with minimal promotion because people will share your posts and articles and do most of that work for you. However it can also be a headache to produce content, particularly if you find yourself fretting over how long you should make your posts and articles.
When it comes to blog content there are two schools of thought on this subject. One says to write lots of fairly short posts and articles and post often, as much as 10-20 times a week. The other says to write long articles and only post a few times a week. Both sides believe very strongly they are right about how to write.
Both methods have drawbacks and advantages.
Most people don't really like to read long posts and articles unless it's a topic they really care about. Plus every time you post new content your site (should) be letting other sites know it's been updated. Since the blog directories and search engines like sites that update often, that can be helpful. So there are some real advantages to writing several short posts through the week.
On the other hand search engines like text, the more the better. As long as you aren't just stuffing your writing full of keywords at least. Plus people tend to value longer posts and articles more than short ones. You might not have as many people reading them, but those that do will appreciate your efforts a great deal. So there are also distinct advantages to writing longer posts and articles.
I prefer to take a different approach altogether. Personally I tend to write things that are to the point. It caused me trouble in school when a teacher wanted an essay on a subject. I would write the essay, but would often get marked down for not getting it long enough. I tended to condense what needed to be said into as little wordage as possible.
I have since improved on my ability to expand on things I am writing about. However, I have found my preference for writing blog posts and articles is to just dig into a topic and see how far it takes me. I don't set out to make posts or articles of any particular length, I just write until I don't have anything else to say. Generally I write out a first draft then go back to it a few days later to expand on the initial ideas and points I set down.
Maybe I should be more focused in my approach to writing, but I feel like my style fits me well, and has worked okay for me. I don't have to worry about padding out my posts and articles, or trying to condense when I really have more I want to say. I just write what feels best and live with it.
I think that is what's really more important than making sure you hit a certain length for your posts, or post often or not. Being true to yourself will make sure you always write things that are speaking from your heart, not your desire to appease the search engines, or readers with a low attention span. If you really want to write about something you shouldn't have to worry about how long to make the post or article, it really isn't fair to you.
Really the choice is yours. No one can really tell you what the best way to write is, since they aren't you. We all do things differently. Some people are good at writing a lot of posts and articles by breaking down the topic into chunks, some prefer to tackle a subject and really say everything they feel like saying at one go. In my case I just write what I feel like writing.
So you really need to figure out what style fits you best, rather than thinking there is really a right and wrong way to write articles and blog posts. You will find yourself having an easier time producing content and will actually enjoy the process more.