well, there in lies part of the problem with a small 3 man team… the codex is where we want to document the complete list…
you can find a partial list at: http://codex.simple-press.com/codex/api/actions-filters-and-classes/ but its already out of date…
the easiest way to look for our actions, hooks and filters is in the code itself… do a search for do_action or apply_filters…
if you have content and you want to filter it some way, we may have a function for that already… all of those kind of filters (unfortunately, name confusion), you can look in our filter api file simple-press/sp-api/sp-api-filters.php
but… if you just want to display the latest topics on your home page, you dont need a filter for that… you want a template tag or widget… so grab the template tags plugin and see if the included widget or one of the template tags will do what you want… see our footer for couple examples…