Personally, I'd be more interested in unique creature designs over "generic" anthros, so I'm not sure if my feedback is that useful (and even so, the few adoptables I already got are still pretty much just gathering digital dust somewhere in my old folders...)

I like the pose and especially that you added the backview and "thiccness slider" in the other post ;-3
Most template-based adoptables I've seen are somewhere in the range between 10-50 for simple ones and up to 100 for more complex, so I think your estimate is pretty ok. I'd go with flat price for simple ones, but wouldn't hesitate to make more of those with similar patterns and colors - if more people like one particular design but only one can get it, the others might still opt for a similar one that's "close enough". I'd reserve auctions only for the more complex and unique designs (and post them separately to avoid confusion), but offering both I think is more flexible than only one or the other.
You could also try several price tiers with addons on higher tiers - like tier 1 - only base design with front and back, tier 2 with added headshots (I'd go with frontal and side with these to complement the angled body views), tier 3 with added detail shots on whatever bodyparts are of special interest, extra wings or whatnot, etc.

Also checking out galleries or directly asking artists who do a lot of adoptables might be helpful too, from the top of my head I think  seskata and  jakkal did quite a few