Wow, eight inches is a lot. I realize you have entirely different weather than I do (no snow or mud seasons here, the ground doesn’t freeze, etc.), and probably entirely different soil, but that’s deep, at least to me. We have pea gravel for our paddock, and eight inches of that would be difficult to walk on/in.
If the surface is scraped, what can you get down to? Anything more suitable for a base?
You’ll only have two horses, correct? Do you really need the quarter acre, assuming that they’ll have additional pasture time? Our turnout was originally made to be about 70% of your planned size. When we got down to two horses, we eventually subdivided it 45/55, which has been perfect. Still plenty of room to walk, trot, and even canter if the mood strikes in the 55% section, but less upkeep. We did not have to add a base or fabric, due to our natural soil, and have simply topped off with a load of gravel every several years (don’t you plan to sell in five?). We turned the smaller section into an irrigated area of grass, which has been a boon in times of drought, when the pastures can’t take any grazing whatsoever. Of course, I’ve always had smaller horses.
Best wishes with whatever you decide.