I will be renting ADU fulltime and will not use for personal usage.

So, if the surviving spouse is on SSI, they may be able to do back and document their change in living circumstances showing they were splitting rent with someone before but that person died so now they have to pay it all.

I used an FHA loan but I am concerned about accepting rental payments into my personal bank account. 

The factors to consider are your overall objectives, your credit score, DTI and personal financial condition I recommend you find a broker or originator whom you can trust and have them weigh your options.

Move-Out Checklist for Investment PropertyA well-structured move-out checklist helps protect your investment, ensures a smooth tenant transition, and reduces turnover costs.Tenant Responsibilities (Before Move-Out)✅ Provide written notice of intent to vacate (per lease terms)✅ Schedule a move-out inspection (if required)✅ Pay all outstanding rent and utilities✅ Remove all personal belongings and trash✅ Clean the unit thoroughly:Wipe down walls, baseboards, and doorsVacuum and mop floorsClean kitchen appliances (inside/out)Wipe down cabinets and countertopsScrub bathroom sinks, toilets, showers/tubs✅ Replace any missing or burned-out light bulbs✅ Repair any tenant-caused damage (holes, broken blinds, etc.)✅ Return all keys, garage remotes, and access cards✅ Provide a forwarding address for the security deposit refundLandlord/Property Manager Responsibilities✅ Conduct a pre-move-out inspection (optional)✅ Take photos/videos of the property’s condition✅ Verify all keys, garage remotes, and access cards are returned✅ Check for unpaid rent, utilities, or damages beyond normal wear and tear✅ Hire a cleaning service (if needed)✅ Complete repairs and maintenance (paint, flooring, appliances, HVAC, plumbing)✅ Change locks if required by state law or property policy✅ Test smoke detectors and carbon monoxide alarms✅ Review lease terms for security deposit deductions✅ Send tenant security deposit refund (minus any deductions) within the legal timeframe

So your personal life will be cheaper, less regulated, less taxed, and less wasted in traffic.

Add calendars so my investments are separate from personal but make it better.

You could use an LLC, Trust, personal name, etc. 

My lender who I've personally worked with for over 5+ years now.

The answer is its personal preference.