Is the self all that can be known to exist?

[Angrboda]

"This statement is not true." has the same structure as "This sentence has five words."  

I wouldn't say that. They have different syntax. The former is definite article-noun-verb-adverb-adjective. The later is definite article-noun-verb-delimiting adjective-noun. If we take both as propositions, the first is about the proposition as a proposition, whereas the second is a proposition about the form of its expression. I believe those differences are relevant.

It's a question of how you partition it. Regardless, substituting the sentence, "This sentence is not long," obviates your objection and my point holds.