I don't know if you are aware of this but the Attachment feature for posts only allows one primary URL to be attached. A workaround I found was to make a threaded post. Make the initial post have the attachment you want people to see first. Then to get the code for a second attached website, start a new initial-post, build the second attachment as you did the first, then copy the code you see in the body, then paste that into a top-level comment of the previous initial post. You can also organize topics by adding Categories or Hashtags to your content; viewers on your profile can filter all your posts by those organizing principles. See the left panel of the profile of @Michael Rupp
Adding the Categories and Hashtags by editing an old post works too.

Also, I'm not sure if you are aware of the "markup language" for making better posts & comments.
Friendica BBCode tags reference