If so, what is the historical vacancy rate for this property? 

I would you advise for you to revisit the terms in which where you found the deal to be most attractive and add in additional contingency plans and vacancy rates to make sure you're security your purchase.

Specifically, what percentages do you use for vacancy, repairs/maintenance, and CapEx.What are your cash flow and ROI goals?

You may need that 10k as the market turns and you end up with vacancies or nonpayments with your duplex.

I own 100+ portfolio in Mississippi with 0 vacancy.

. - on-going communication with tenants and you,- move in and out inspections and reports,- monthly reports (may be financial),- monthly survey,- co-ordination with contractors, maintenance crew, cleaning staff,- taking pictures and videos, - using the management tool you provide, - picking up supplies, - 24 hours on-call,- ensuring paperwork/leases are complete, - issue notices, writing notices and posting,- ensuring low vacancy, ensuring high rents,- resolve issues,- collect laundry money,- be nice and approachable, etc... you get what you pay for. 

You can filter by relevant criteria such as vacancies, cap rates, grms, etc) and can easily toggle to see nearby rent and sale comps!

Your loss to lease on that unit is $100.But, let's say the property you were buying was owned by someone who hated to have vacancy and their is a property next to another apartment of similar age, condition, and amenities. 

NH vacancy rate is much lower than the national average.

(I'm not using these numbers to calculate my ROI or Cap Rate, just to get me through a possible long temporary vacancy if people decide not to move due to this whole virus thing)   The true holding cost would be around $660/month (including principle, interest, taxes, insurance & maintenance).