(1) Are you a visual user or an imager?
Visual only (mainly lunar and planetary) with TAK TOA-150B.
(2) How big is "big enough" and why?
Without permanent setup: 150-180mm, not slower than f/8; with permanent setup or observatory: 180-200mm, not slower than f/10.
(3) Using the old 127mm f/9 Meade ED doublet as a benchmark, would color correction be acceptable to you if it was about the same? A little worse?
I have no experience with it. I consider APO's from TAK, A-P and TEC as benchmark refractors.
(4) How much would you be willing to pay for a (i) 150mm?, (ii) 160mm?, (iii) 180mm?, (iv) 200mm? (That's not a typo - yeah, an 8-incher. )
Speaking of APO's with benchmark quality: 150mm = up to $12,000; 160mm = up to $14,000; 180mm = up to $17,000; 200mm = up to $ 24,000 (If funded to buy... These figures reflect the current price situation, I don't think that this price level may be substantially lowered. At least if benchmark APO quality is wanted.)
(5) Would it be a plus (in the sense that you'd be willing to pay a bit more) if the optics were designed by a well-known designer?
Perhaps. But just a slight surcharge would be accepted.
If the optics were manufactured in Europe?
(6) Is ready availability (i.e., no more than a 3 month wait) a major plus in your view, or if the price were a bit lower, would you be willing to wait a bit longer?
Waiting time not more than 6 months please. A-P-style 10year waiting list system is a total NO-GO to me.
(7) What would you think about the manufacturer designing the refractors so that they use ultra-light materials (composites, magnesium and titanium fittings, etc) so that a CGEM/Atlas class EQ head could deal with the moment arm?
Without importance to me.
(8) What would you think about the manufacturer offering pier assemblies of appropriate height, set up for common EQ mount heads (again Atlas, CGEM, CGE Pro, G-11, etc.), to accommodate the length of the OTA?
TAK does this, I highly appreciate it.
(9) What if the manufacturer also offered hargreaves struts for the tube assemblies?
I don't have an opinion on this.
(10) Would a modular tube be desirable even if it drove up costs a significant amount (i.e., the tube breaks into 3 sections, fits in a matched hard case, and fits in the back of the average compact SUV (Forester, CR-V, RAV-4, Equinox, Escape, etc.)?
Not interested in modular OTA's.