The general rule of thumb on bipe design is that the upper and lower wings should separated by the chord of the smaller wing. But, that is just a general rule. I forget what the exact rule of thumb for tail surface area is supposed to be, but I think it's 33% of 75% of the total combined area of both wings. Example. If the total area of both wings combined is 1000 sq/in's, then the tail should be 33% of 750 sq/in's = 250 sq/in's. Chuck Cunningham went over this many times in his RCM column so I'm sure there is someone around here who can confirm or deny that formula. CG is determined as by plotting out the stagger of the two wings, compare area between the two and measuring back aprox. 25-30% of the average chord. For the engine. You have the engine mount so a quick measure meant of the beam width should give you an idea on what size to use. Then again, the mount may be marked as 40-45

With the amount of measuring and figuring you have in front of you, there's a very good chance you will have something to be very proud of once it's in the air.

Good luck,
John