for our smallest property he did some quick calculations and came up with approx. $150k hit on a $550k sale price. 

BiggerPockets also has a calculator to analyze deals, and I highly recommend you start this as soon as possible, even if you are not ready to buy.

Cash flow and taxable income are separate calculations.

Unless they allow future rental income to count towards the DTI calculation.

Did you calculate the value of the time you spent on this?

At closing the taxes will be calculated per day and then divided by days remaining in the year at closing.

Put together a spreadsheet using the bigger pockets calculator.

You can lookup the tax rate on the county assessor website - Make sure you are looking at or calculating the property tax WITHOUT any exemptions (since you’ll not get any as an investor). 

Some owned are inside ROTH IRA'S so I will never pay or owe ANY tax or capital gains on the profits.Some are 1000% tax free profit, before adding in the accumulated tax free rental income, If you finding better investments, I'd love to hear the details.I tried to use a financial calculator once, it just got real hot and burst into flames.

Or am I doing sny wrongI'm using the BP calculator