I mainly want to ask if these assumptions are reasonable and if there's anything I haven't considered:(1) multifamily units in NJ close to New York City, ~$1,000,000, 20% down payment, (2) Using the following assumptions: 4% appreciation rate, 6.5% interest rate and 5.0% refinance after 5 years, $10,000 yearly maintenance fee(3) ~$6,000 monthly rental and assume 3% increase yearly with 5% vacancy rate(4) Based on the above, the calculated IRR if selling at the 10th year is ~19% (considering tax benefits) and ~17% (without tax benefits).

You'll want to put together a personal financial statement (basically lists of all your assets and liabilities) and have your tax returns ready.

Taxes have to be paid, so does insurance, what about maintenance? 

And you would get to indefinitely defer all tax on the gain from the sale.

that we’ve learned in our 24 years, managing almost 700 doors across the Metro Detroit area, including almost 100 S8 leases:Class A Properties:Cashflow vs Appreciation: Typically, 3-5 years for positive cashflow, but you get highest relative rent & value appreciation.Vacancy Est: Historically 10%, 5% the more recent norm.Tenant Pool: Majority will have FICO scores of 680+ (roughly 5% probability of default), zero evictions in last 7 years.Class B Properties:Cashflow vs Appreciation: Typically, decent amount of relative rent & value appreciation.Vacancy Est: Historically 10%, 5% should be applied only if proper research done to support.Tenant Pool: Majority will have FICO scores of 620-680 (around 10% probability of default), some blemishes, but should have no evictions in last 5 yearsClass C Properties:Cashflow vs Appreciation: Typically, high cashflow and at the lower end of relative rent & value appreciation.

If you are taking out a conventional mortgage of any kind, you can't buy in the LLC as it does not have two years of tax returns.You are also asking if an entire state is good to buy multifamily, which means you are too soon in the process to even talk about buying.

What about the utilities, property taxes, maintenance and repairs, capex, etc. are any of those optional for you?

I have gutted to the studs the last 5 properties I have bought from tax/foreclosure sales in this county and this one is not far from a full rehab. 

Generally speaking, with SFR or small multis, I just rely on the lease/rent roll (and some form of proof of payment; i.e. bank statements, deposit receipts, tax returns, etc.). 

A 4 bedroom would have you competing with larger condos or townhouses with pools, a much lower rate of return.