[Carnage]

To further explain 2:

If I release 5 mods. They each have an install count. Member A might have installed 4 of my mods, whereas member B only 1; the current count would say 5 total installs. The statistic would be count("select distinct userid from installs where developer = 'Carnage-'") giving the number of unique members that have installed at least one of my mods.

As for 3, display it along side the similar threads (above or below or to the side) Extracting said information is simple enough: "select distinct modid from mods join installs on modid=modid where installerid in (SELECT installerid from installs WHERE modid = 'this mod')" you could do something fancy to order that query by installs and display the top 5. Depending on the table structure could be a little heavy as a query; might be prudent to cache the results for a day or so.