My reluctance is that it is in an A -A+ neighborhood and everyone I've listened to has said that it is best to buy in a B-C+/blue collar neighborhood so that your chances of keeping a longer term tenant and avoiding annual vacancies will be low. 

Depends on your long term goal and if it cash flows/maint/vacancies/appreciation, etc

Determine how much you could charge for rent and how much your expenses would be (including mortgage, insurance, property management, repairs, capex, vacancy, etc). 

I use 8% as vacancy which is 1 month out of 12. 5% vacancy is 1 month out of 20 .

I have two buildings under contract, that host 25% vacancy, and a traditional commercial bank will not finance them.

Make sure you can make a case for the projections that you are making and be sure to include realistic vacancy factors and rents.

but I placed them in an expense/cost section along with water/sewer, trash, heat, electric, vacancy, management, maintenance, and capex.

I'm sure it will appreciate well over time since ADU's are still new and in 5 years there will be more properties to compare it to for appraisers - but we are not comfortable with covering vacancy costs that could be up to 7k per mo.

I think the economies of scale of multi family and not having a single vacancy or repair eat up all profits in a year are very good reasons to go with larger multi family units.

I have ran all the numbers, including PITI, vacancy, maintenance and CapEx, and it would just barely cashflow.