high frequency low voltage Push-Pull topology

Hi,

I need to design a custom transformer with dual primaries and dual secondaries. The application is:
Push-Pull topology, running at 1MHz.
Output approx. 5W, 14V.
Input 24V
Controller: LT3999

Reading between the lines of what LT have done with their demo board, minimizing leakage inductance seams important, I guess to avoid having to use lots of lossy snubbers.

Given this, what is the best winding of a push-pull transformer, assuming that there is a layer per winding?

Do I need to put the primaries on top of each other, if I do a PSPS split. Would it make any difference?