A HYSA pays 4.5-5%(before rates went down) pre-tax, 3% net tax if you're a high earner. 

No but keep track of those repairs as it will add to your cost basis when you go to sell it and have to pay capital gains.

I will not comment as to the tax laws and underlying rules - that is a discussion you can have with your tax advisor who presumably you are paying to help you.What I will do is provide practical and business guidance on tracking time.Firstly, there are apps available that can assist with time tracking where you can specifically detail your time, who you met with, etc.

In reality, you are going to be the one to pay for that.  

In addition due to prop 13, the tax base is a fraction of if it sold today.   

Whichever loan that you decide to use, the interest will be tax deductible due to interest tracing rules.

When we looked at what his cashflow is currently, and then considered what he would net out of a sale post tax, he decided to keep owning the properties.

A 1031 exchange would use all of the tax in the purchase of your next property.

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).

The 1031 exchange will indefinitely defer all tax on profit and all depreciation recapture.