OR, by all means, insert your comment where it seems to fit best:
you may want to inset it with a bullet and/or set it in italics so it's clear (always sign and date)
if a sub-topic develops, separate it with a horizontal rule at beginning and end
A good format for a new topic is "dissertation followed by discussion":
start with a brief, factual introduction, followed by double horizontal rules
let the discussion begin
When a discussion dies down and the page becomes static, if you're clear on your course, feel free to refactor mercilessly:
fearlessly edit down to capture the key points
reduce the noise without losing the facts or the flavor
if you merge or delete comments, group credit Contributors: at the end of the page
This is how Wiki content matures and grows in value over time.
For external site links, you can type URLs directly into the text - http://etcete.ra/... - it'll clear to anyone where they're headed on click.
TWiki is intended for world-wide use, and an international standard date format like 01 Sep 2001 is preferred. It's universally understood, and clearer than the xx/xx/xx format, where a date like 9/1/01 can mean either Jan or Sep, depending on the local conventions of the readers. For months, use the first three letters: Jan, Feb, Mar, Apr,...
TIP: Check the source when you want to find out how something is formatted: click Edit on the lower toolbar. To see earlier versions, click More, then check Raw text format and click View revision. A bit of HTML experience can't hurt, but you'll soon see with TWikiShorthand how far that is from necessary.