US payroll setup for nonresident alien employee (Japan-based, O-1 visa) - CPA / EA preferred

We're an early-stage US C-corp with one employee to set up: a Japanese national on an O-1 visa, tax resident of Japan, working mostly from Japan with occasional US business trips, relocating to the US within 6–12 months. Note: this is a nonresident alien (NRA) working abroad - NOT a US expat abroad. If your experience is with US citizens overseas (FEIE, Form 2555), this is a different situation. Scope - two phases: Phase 1, setup (~5–10 hours): 1. Confirm the withholding approach: wages for Japan workdays paid gross (not US-source), wages for US workdays subject to withholding - and document the workday sourcing method 2. Determine FICA treatment under the US-Japan totalization agreement 3. Set up the NRA W-4 correctly (special NRA rules) with a foreign home address on the W-2 4. Recommend the payroll mechanism (payroll platform that supports foreign addresses vs. manual 941 deposits + year-end W-2) and configure or document it Deliverable for Phase 1: a short written setup memo documenting the approach, then transition directly into running monthly payroll. Phase 2, ongoing (monthly, est. 1–2 hours/month): run payroll each cycle — compute the US/Japan workday split from a travel calendar we provide, calculate withholding on the US-workday portion, process payment, handle 941 deposits and filings, and issue the year-end W-2. Continues at least until the employee relocates to the US (6–12 months), likely beyond. How we work: async-first (email/Upwork messages), founder is in Japan timezone (JST) but flexible for one or two calls. We move fast and respond quickly. Screening questions - please answer all three in your proposal: 1. Have you handled payroll for a nonresident alien employee of a US company performing services abroad? Describe one case. 2. For an NRA whose services are performed in Japan, are those wages subject to federal income tax withholding? Why or why not? 3. Are you a CPA or EA? Please include your estimated hours for the setup scope. We'd like to start within 2 weeks.