Lubuntu is very light and is actively supported.
Regarding the JRE, I don’t know what the ‘correct’ version to use is now 
The old version 6 ‘Sun’ version is no longer being developed; the ‘official’ version 7 is the OpenJDK one (but I don’t know if this works 100% with Ignition); and there is also an Oracle version 7.
If anyone from Inductive reads this is would be nice to get a definitive answer.