Welcome to the forums! It looks like you have a nice little car for hypermiling and sounds like you are on the right track,
except HHO is proven to be false.
If you search the Ecomodder website and read about HHO, you will find many examples.
As for the driver 10-15 kilo weight reduction, you will find you get many more miles out of him as well
Take it from someone who lost ~20
Anyway welcome, and don't worry too much over your English. You seem to do quite well, and everyone here is friendly and understanding.
~Matt