You can also work from the HTML end, if you’re not trying to incorporate images, and load an HTML file in TextEdit, which renders it into rich text while preserving formatting and links.

Here's how you can select different pieces of text and copy them at the same time in TextEdit.

Occasionally, maybe once every few weeks, TextEdit refuses to save any documents I currently have open. Any changes I have made to these documents seem in danger of being lost. When this symptom ...

For some silly reason, OS X’s TextEdit app’s default format is rich text. If you prefer plain text, Defaults Write points out that you can easily set that as your default with a Terminal command.