1k will be good.

Personally, I find it easy to ramble, so I could easily get posts that go overboard. I always assume too long of post will cause everyone to skim it rather than read, so I try to keep mine between 2-4k. But that is me. If you do small snippet scenes, you could pull off something like 500 or 750 words. 1k is probably best, but if you are writing complete scenes you'll probably want to get at least 1k.

The important thing is the ability to convey the details and character decisions in a way that is believable, and that you are descriptive enough for us to know what exactly it is you are describing.