Just enough to burn black things and pop balloons. I'd probably let it cool a minute between burns. Ans I really hate things like that; I've never used a hot glue gun. My dad could solder it, though.
A 16x DVD burner diode needs some heatsinking. The lens does not help here. The aixiz housing provides some heatsinking, but more will be needed. Some creativity with washers, etc. helps here. If you somehow have access to a machine shop (school, work, somehow) you can make a custom heatsink to fit your host.
As far as driver current, maybe do a search on 16x dvd diode, read the postings over, and decide what setting you want to use depending on whether you want long life or maximum burning.
I can take it to Home Depot, and find some fitting washers that I'll glue together. And I want it to last a long time, so I guess the lowest MA possible and still be able to light matches, pop colored ballloons, and melt black stuff.