Close enough is OK, but things like the wing dihedral and airfoil being equal both sides, the tail and vertical stabiliser being at 90deg to each other/fuselage are flight critical as is using as little glue as possible, especially on the tail and fuselage.
Clean cuts are done with a good steel rule and very sharp cutting blades. Bevel cuts are particularly hard with anything but a totally fresh knife, you can use a steel rule set 1/4” or less back from the cut to steady the blade and make a nice true edge. Rolling exposed foam edges with an iron is a nice detail too.