What other careers within real estate do you know of that benefit from having your license?

They could consider doing an exchange to a DST which is 1031 exchange eligible, but would provide managed real estate (completely hands off), but they still get the income off the DST along with the benefits of real estate (such as depreciation).

@Jason SternThe Solo 401(k) is going to provide the maximum benefit as far as deductions and flexibility with future investments.Since you are maxing out your $18,500 contributions in your current plan, you would not be able to take advantage of employee deferrals in your own separate plan. 

There are so many benefits as an investor to having access to MLS, comps, seeing any property any time I want, negotiating with listing agents myself, etc.

That is especially true with the tax law change that went into effect this year; the standard deduction nearly doubled, so the taxes you save by itemizing might be much less than they were in the past (in other words, because you are getting a larger benefit through the larger standard deduction the "cost" of not having the mortgage interest deduction might be less).I can see an argument for there being better uses for your money than to pay off a mortgage with a 5.5% interest rate (if you can make an investment that pays at least 6% for example), but if your quality of life will improve because you paid off your debt and are now "financially independent" then that is what you should do.

Because it is a duplex you may benefit from looking into other banks in your area, especially small banks and not the big names.

Properties in Wellesley and Weston are roaring high in the past decade and sometimes makes more returns than a multi-family, and it is easier to keep its value when there is financial down-turning.I understand that it is totally a personal choice based on the financial situation of a family, personal preference, and personal understanding and sense of risks/benefits with regarding to such choices.

@Justin R.Your CPA is being moderately conservative, and your QI is being extremely conservative.Nothing is wrong with either approach - as long as you knowingly choose the relative safety of a conservative approach over the financial benefits of a more aggressive approach. 

There is often a legal notice published for the benefit of the decedent's creditors. 

Honestly with your lack of experience, you would really benefit from an experienced agent to show you around a home.Even if you have your real estate license, they don't just give you a magic key to let you into any house.