Is there a place within Google webmaster tools where you can find out the last...

...time your website was indexed? I understand that Google indexes sites every three months; is there a way I can find out when it last occurred?

When I use the Google webmaster tool, it only shows my website containing 12 pages, and I actually have 80. In the last three months I have added tons of internal and external links and have installed a "sitemap xml file" that I also registered with google.

When they index again, will all 80 pages show up in the webmaster tool (as they were included in the sitemap xml file). Also, the webmaster tool says I have 500 links, and I have added several thousand; when they index, will this be reflected?

Does your website itself (your hosting company) have a control panel? Mine, for example, has "cpanel" (which a lot of companies offer) and on which there is a "latest visitors" log which you can open, and look for "Googlebot" now and then to find out when Google takes a peek at your website.

Google is crawling and indexing sites all the time. The 3 month thing that you are referring to is Page Rank which is re-determined every 3 - 4 months.
Now you say you have all these links. Are they outgoing links or incoming links.
Outgoing links count for nothing.
The only links that matter are those that are on other similar indexed sites of a decent page rank that point to your site.