Pumpkin pie filling way too thick

You may use all sorts of pumpkins and squashes (a Cucurbita moschata or Cucurbita pepo may be called either, depending on variety) to make a pie. The Halloween types may not be the best choice: they tend to be stringy, not very sweet, and sometimes over treated with pesticides. Instead look for the small varieties (around 5 lbs.) called Sugar, Long Pie, or Trickster.

When making the pumpkin purée for a pie from scratch it is important to deal with the water content of the pumpkin. After you bake, cool, and purée the pumpkin, you may need to use a cheesecloth to wring the purée.

Safe? Or good to eat? Pesticides usually don't penetrate thick-skinned produce (oranges, etc), so as long as you're not using the skin, there's not a lot to worry about.

They're not the best pumpkins to use for other reasons (linked in comments). In summary, the smaller "sugar" pumpkin is better for cooking, if you have the option.