The lattice enthalpy of sodium chloride is 789 kJ/mol.

Ionic Charge and Ionic Radius - the smaller the radius the greater the lattice energy. The charge of the ions is what affects the lattice energy.

Indeterminate. If the atoms form a perfectly mixed solution then you might guess 2a+4b where a and b are the fractions of A and B. But if they form a super-lattice where the stacking of the atoms only repeats over a long range (as happens in the many structures of silicon carbide [silicon and carbon are not metals]) then you can get almost anything, with various seemingly unconnected sequences and lattice lengths, even in different directions. For very dilute things like A50B you will get the normal lattice period of A over much of a crystal but with lattice distortions around the occasional B atom. That would cause a broadening of x-ray diffraction patterns.

Crystal lattice. lattice

In physics, the reciprocal lattice of a lattice (usually a Bravais lattice) is the lattice in which the Fourier Transform of the spatial function of the original lattice (or direct lattice) is represented. This space is also known as momentum space or less commonly k-space, due to the relationship between the Pontryagin momentum and position. The reciprocal lattice of a reciprocal lattice is the original or direct lattice.