"Schaden" is roughly "harm". "Freude" is just "joy". So, no, Schadenstartup doesn't make much more sense.

I tried to think of a phrasing that would work for the idea, but nothing came to mind with a similar ring to it. In kind of faux German, Startupschadenfreude, being sure to pronouce "Startup" as "Schtartup" might be amusing. :-)

No, that just means "damage startup."