Can I Post The Same Article To Multiple Locations?

This is a big NO NO!. Duplicate content (copied content) is one of the fastest ways to get your site de-indexed by Google. If you want your site to vanish from the searchable Internet, link to some bad content or create copied content on it by all means.

The same goes for copying other people's work. It WILL get noticed and you can't do it. Don't be lazy, create something fresh and you will earn.

Let's read a post from Scottdogg187 which really puts things into perspective for you: https://my.wealthyaffiliate.com/scottdogg187/blog/how-duplicate-content-can-hurt-your-rankings-in-google

How Long Should A Post Or Article Or Page Be?

It's up to you, but 400 words should be the minimum. Anything shorter and Google will deem it not very valuable.

On the other end, don't write it too long either. I would say 800-1000 should be your maximum length. Yes, sometimes you will need longer (my WA review is about 1,100 words), but unless it is a review page or a particularly awesome theme page, you are probably waffling when you go past the 1,000 word mark.

Tell your Grandma to get away from the keyword, and cut it down to a better size.