Stanislavz, - Love your enthusiasm, however nothing beats proper research and planning. Are you Croatian?
Jim Marske's manual is good up to a point, but he fails to address buckling (Beam Buckling) of the Web. All Beam Buckling formula are on the Internet, I don't have it in front of me. You will find a Spar will start to fail in the Web, taking the Caps with it, the trick is to take the Web strength beyond that of Possible Buckling. Pretty logical really. You can't beat the Carbon rods for weight and strength
Carbon is light and strong, but fails catastrophically, great weigh savings can be made with Carbon, but hand lay-up it's about as strong as S glass, but much stiffer.
Remember the more weight you save on glass the more weight you save on resin.
On Foams, a good European standard is Divinycell, Last-A - Foam (LAF) crumbly structure - easy to sand, poor for bonding. You can bend Divinycell easily by heating it. Is is stronger in all categories except compression strength, get samples and test them.
There is already a discussion on Mazda Engines on HBA, have a look for it, however there are other discussion groups which address the issues on conversion. Personally I love the Mazda Rotary engine, just wish it were Lighter and the promised PSRU was available at this point in time for those who need it. All comes to he who waits. Be very careful on what you settle for in a PSRU.
The Vision Plans build Aircraft manual has good information of plies and their orientation, plus a great deal of other information you could transfer to any other design, provided it's in the same size and weight range. You could convert those Glass materials into comparable Carbon Weaves, if you wanted to save weight - all available at Spruce Supplies.
Hope that helps.
George