Hi Cindi, I hope that you enjoy yourself here on Steemit and I hope that people actually bother to read your posts and/or comment on them. Maybe you could read this post https://steemit.com/steem/@himshweta/11-things-no-one-will-tell-you-about-using-the-steemit-platform to help you to get a realistic view of what Steemit is like. I think that most people are here to make money, rather than form a community and "constructive criticism" isn't something that you're likely to get unless your pre-exisiting fans have joined the site. I'm not trying to be harsh just speaking from my own experience as a writer posting my original content to this site and getting absolutely no response to it AT ALL (but that's explained in the post I quoted.

As to the character or word limit, I haven't noticed one but most writers seem to write quite short posts which I would say are less than 500 words.

You can post pictures that belong to you and if you do post other people's pictures then I would suggest that it is necessary to get permission from whoever holds the copyright seeing as you can earn money from your posts on this site.

Basically I would suggest that you do whatever you would do if you were publishing a book, ie use your own material or gain permission from the copyright holder. As posting to Steemit without permission is copyright infringement unless your post somehow fits the Fair Use clause.

The points system is mentioned in the FAQs, at least I think it was when I read them but there are various posts on this site which can give you more easy to understand advice.