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The key advantage a long focal ratio newt has is the smaller secondary obstruction over the equivalent SCT. A well designed f7 newt can have a reasonably sized fully illuminated fov with a 20% obstruction, compared to the typical 33% of a cat. Trade off is mounting the optics grows exponentially more difficult with size.
There are many parameters involved but putting it simply, more aperture gives more resolution (notwithstanding seeing conditions) and smaller obstruction improves the contrast. You want both.
Making a good mirror suitable for planetary work is not easy or simple. It will be the third or fourth mirror you make. Only take mirror making advice from someone willing to let you look through one they've made.
Regards,
Andrew.
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