Hi Damien,
I can only help you with one of your questions.
I recently acquired a Moonlite (manual version, tri-knob) for visual use with a Meade LX200-ACF 10". During my deliberations, I obtained the illumination and vignetting analysis for Celestron SCTs from the Yahoo SCT users group and interpolated for a Meade 10" SCT (though I doubt that made any difference as the conclusions were clear enough).
As measured by me, the LX200 10" baffle ID is ~51mm while the SCT adapter opening is ~40mm (a tad bigger than Celestron's 38mm). For visual with a wide-field 2" eyepiece, the penalty of adding a Moonlite with 3 1/4" flange is moving the focus point back about 100mm compared to an SCT diagonal, which induces vignetting of (IIRC) ~4% and a slightly smaller TFOV due to longer FL. However, decreasing the baffle opening from 51mm to 40mm induces vignetting of around 35-40% (my interpolation), with the effect being most noticeable at the edges. The effect of additional backfocus of that order is negligible compared to the smaller baffle opening.
For imaging, the additional backfocus should only have a relatively small effect, but I'm no expert in that area. The effect of the additional ~30mm for the tall FR style flange should also be virtually negligible, IMHO.
Be careful with focal reducers. Does the GPS have ACF optics or standard SCT optics? My research in that area is far from complete, but for ACF optics, only two look promising - the Optec Lepus 0.62 Telecompressor and AstroPhysics CCDT67 - the Meade and Celestron 0.63 FRs don't work with the ACF optics but will be fine with standard SCT optics.
I've been impressed with the build quality and performance of the Moonlite. Although the mirror flop in my LX200 isn't too bad (compared to others' reports online) nevertheless, achieving good focus using only the "coarse" focus knob was virtually impossible, whereas it's easy and repeatable with the Moonlite even with heavy diagonal and eyepieces. The Moonlite's fine focus knob works smoothly enough (and with a light finger touch) that I see no particular advantage for visual work of an electric focuser. Imaging may be different, however.
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