Since "to ciekawe" doesn't have a verb, couldn't it be translated as "Interesting"?
I thought I read early on that "to" can only be used like this with nouns. Is that just wrong, or am I missing some other point?
it can be only used with nouns in the sentences with subject like książka jest ciekawa but it is used in "this is" sentences,
OK, thanks, so if I have this: "książka jest ciekawa" is correct, "książka to ciekawa" is wrong, but "to ciekawa" is ok, talking about the książka?
no. To ciekawe can only be in neuter, and it is about something said, described, something happening, something you see. It is about a scene, a sentence, not about an object.
You can say to ciekawa książka, or jest ciekawa or ta książka jest ciekawa
When you want to say "to" and it's followed by an adjective, is the adjective always neuter?
Yes... my understanding is that "to + [adj]" can only be used to talk about something abstract, and the adj is always in neuter form. But as immery says above, you can also say "to + [noun phrase]", and if the [noun phrase] starts with an adjective, it still goes with the gender of the noun.
So: "to ciekawe" (for abstract things only), but more generally "to ciekawa książka"
All right, but if I wanted to say "it's amazing," could I use "to świetnie" or " to świetne?"
świetnie, used by itself is an adverb, but "to świetne" as an adjective