I would supplement your fair advices:

• In Google you must use free images (sometimes it is not enough to mention the author); to do so, you can use the advanced filters
• It could be recommended to obtain an author's written permission (or such a proof) for using part or entire of his work/images
• Steemit is a social based on quality: why should I read anything already written otherwhere? So, write new/original content, do not copy, nor re-elaborate summaries (spun); even if you are the author of a text published somewhere cheetah may catch your work and mark it as plagiarism. So post here first, then in your other blogs/socials if you want
• You can copy sentences that are already written by anyone using the blockquote html tag