Getting a handle on gnus

[Les Harris]

I've spent the past week slowly coming up to speed with gnus.  I'm at
the point where I can pretty much use it in a basic way and am wondering
why I haven't been using it for years.

I can't seem to figure out from the documentation or elsewhere a couple 
things though:

1) I like topic mode. How do I make it the default mode on startup?

2) What is the difference between 'g' (Check for new news) and 'alt-g'
(Fetch new articles). 'alt-g' does what I want, can't seem to figure out
what 'g' is doing. A corrollary: How can I fetch new articles on gnus
startup?

3) How do I go about automatically fetching new articles on some
constant time interval? (Something with a gnus daemon...?)

Any pointers to documentation or outright answers very much appreciated.

Les