I am new to this hobby and by no means an expert,but the shallow
prop setting is called a surface drive and seems to be desireable for higher speeds,but if you can find pictures,you'll see the
prop is quite a few inches away from the rear of the boat,yours being as close as it is might cause some kind of cavitation issue.Your
prop issues may be balance related,and the odd surface area shape may cause more drag than propulsion,it appears to be bent at almost a 90 degree angle,I would try notching the bottom of a flat piece of material and welding it at a 45 degree angle on the shaft tube,overall
prop size would probably depend on the boat length,but I don't know enough to even guess how big to go.
Good Luck!!! CB