How much did you pay for the land?

Usually we have a few thousand dollars each year to invest after we max out these accounts (and it usually just goes into a taxable brokerage account where we use it to buy Berkshire Hathaway or Markel or some other stock that does not pay a dividend).That extra money was actually how we ended up buying this duplex - thought it might be a good way to diversify our investments.I was wondering if I could use net income from our duplex (assuming we have net income, and by net income I mean what we report to the IRS) to fund a solo 401k or some other kind of tax-advantaged plan?

I usually tell my investor clients that if the building itself will be in a flood zone (not just parts of the lot), it's not worth the investment unless it's a steal and you're able to pay off any mortgage easily if flood rates rise ridiculously (and you can afford to pay for any flood damage, yourself). 

Just like everything else, with cost seg you get what you pay for, and $400 doesn't pay for much.

do we pay a transfer tax? 

Insurance would cover it, I would pay the deductible, and no assets would be lost.If you are in an area like San Diego where people are more likely to sue, a judge is more likely to find you guilty, and the payout is expected to be higher, you may consider an umbrella insurance policy.

You'll pay tax only on what you pull out of the 1031 exchange. 

You get grandfathered into the codes that were in place at the time, you get the old setbacks, you don't pay an architect, engineer, city and permit fees, plan check costs, school fees and other costs that will not come with an existing house.Not saying that you can't build new for less than a remodel, but not usually when you add in all the costs above. 

Be prepared to answer a lot of tough questions about the risks and the process in general.On the plus side, having to pay cash and be at the auction in person usually roots out the "know nothing" buyers that drive prices up.

As an investor and a customer, I don't mind paying a monthly retainer fee, as long as the quality of the service and the communication is good, especially during tax filing times.