Q,1) Would I be subject to NY state income taxes as a fully remote employee?
A. 1) Yes, most likely, NY (or NJ, DE, PA or NE) tax telecommuters, depending on how your situation meshes with the "convenience of the employer" rule. For a fuller explanation, see https://ttlc.intuit.com/community/state-taxes/discussion/re-your-employer-has-reported-this-correctl...
Q. 2) I know I would have to file a nonresident form for NY state. Does this benefit me in any way, tax-wise?
A. 2) Yes. Your NY employer will, almost certainly, withhold NY tax. So, you may get some of it refunded. But "benefit" in irrelevant. You are required to file a state return.
Q. 3) The company I would be working for is in Manhattan. Would I also be subject to the NYC income tax?
A. 3) No. See https://www1.nyc.gov/site/finance/taxes/personal-income-tax-and-non-resident-employees.page#:~:text=....
