Right, Spinoza was a pantheist, so God for him was just nature. Nature isn't fundamentally mental, for the pantheist, since nature has all the attributes, as you can conjecture from the variety of stars and planets.

What could God's personality be? Wouldn't that personality be a limitation? If God's personality is reflected in human ones, that still makes for a wide variety.

We can talk figuratively about the "character" of natural processes in general, in which case we'd have to account for their apparent mindlessness and monstrousness. This was close to Schopenhauer's and Mainlander's point about nature's "will" that creates only to destroy all forms.