Whether you footnote or cite sources is up to you. Footnoting and citing sources slows down your readers, but they make the writing more credible. Unless you are writing for a peer-reviewed journal, or for a publisher who demands that you follow house rules, you get to make the rules for yourself.
Most publishers are not shy about telling you the rules if you ask, and rejecting your work if you don't follow their rules, but when you are self-publishing or working with a publisher that is not doctrinaire, you get to make the rules yourself or make them up with your editor.
Following a style guide like the Chicago Manual of Style, or the APA guide is an easy way to be consistent, but that is up to you or your publisher. I prefer the Chicago Manual of Style because it is a little cooler, but that's me.