Ghibli Park, help with Grand Warehouse time and limited items?

I'm getting ready to get my tickets for Ghibli Park

What's the best time to reserve for Grand Warehouse access?

Is it better to take the first available ticket (9 a.m.) or go around lunchtime (the one at 2 p.m.) so you don't have to lug all your purchases around the park all day?

Also, I read that there are limited items that can run out. Can they only be obtained at the Valley of the Witches? What are they exactly?

More generally, what are the best shops?

by uomofaber