http://youtu.be/vOE2cLRRdLI
/12 is to less. You will have no speed. Remember that this is not a 2stroke with high rpm.
4blade will word, but it costs power. Of course you have enough with a il150.
And dont use gfk or cfk props. Wood is here the better choice. They will make a fine noise in flight.
The il150 works fine with a 28/16 fiala prop.