Intermission: Notes on ている and てある
Progressive ている can also be something that happens on a regular basis, not just at the moment. Like "I go to a highschool".
を with てある is the first of many brainfucky constructions that really mess with western conceptions of subject, object, etc. No grammar instruction will help you understand more than if you did a little reading. Read, read, and read more.
The closest thing to てある for い-adjectives is くある, which is only used in constructions that want to work on the adjective like a verb like 悪くあります, and is wrong or unnatural on its own like in 悪くある. A couple adverb-based constructions like 多くある overlap with this くある, but they're different. You will definitely run into things like 悪くあります, but this is a way of making polite verbal statements with adjectives, not expressing an enduring state.