G'day Mabel,
I think, from my mindset: start simple, start small. Maybe ignore plugins until you get basics of tiddlers and organizing tiddlers via links between tiddlers, maybe "index" tiddlers that are just simple lists of links to other tiddlers.
Of those things you ask about, probably good to figure out "drag'n drop" of URL's into a Tiddler. If it helps, see screenshot below.
I'll let more experienced TiddlyWiki folk chime in on your other questions.
Cheers !