Hello erec,
I have experience with the Zero 50 CC. But every CMP Zero needs a lot of weight in the nose, so the better choice is probably the heavier engine. For my bigger Zero I used pneumatic retract for the ESM La-7. Maybe you can compare some ESM retract, for example Ki-84. I don´t have any experience with any electric retract, so I can´t help you with this question. CMP models don´t have scale length of the legs and diameters of the wheels.