By my calculations your projected weight and wing area will result in a wing loading of 21 to 24 oz per sq ft which is a bit on the heavy side for my taste. Plus with 4 small glow engines of the type mentioned you are very likely underpowered, add the fact you will possibly use 3 bladed props which are usually less efficient at low speed and you appear to be running the risk of encountering significant problems in my opinion.
If you can build the plane to weigh 2 1/2 to 3 lbs max your odds of success will be much higher. Weight is many more times more critical on 1/2a planes than larger planes (except 3D planes).
APC makes a 5.7 x 3 prop that works very well on 1/2a engines and may fit your application better than 3 placed props.