Yes on the first question. If you go to Tools, Stats, you can see an entire list of prebuilt statements and what they extract. Click on "Source" to bring up the html.

Total posts is:

<%GForum::Stats::posts_total%>

Total threads is:

<%GForum::Stats::posts_threads%>

Then you just have to muck about with the category_list.html template.

Regarding your second question, I have no idea. The best I've been able to do so far is put members/total posts onto my main page, I'd be curious to see how a login would be done. Who's online wouldn't be hard though I don't think.

Here's how I present the Total Threads/Total Posts on my category_list template:

http://www.heavybombers.com/forums

And the simplistic stats on my main site page:

http://www.heavybombers.com (top of page in box)