A self-directed IRA would be a great vehicle for you to use for those investment properties. 

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Half the crew are driving company vehicles and receiving bonuses on top.  

I just realized that she has like 3 vehicles on her property.

Everyone thinks that replacing a light bulb should cost $5, meanwhile you have to send out a qualified person on payroll with benefits on a company vehicle, who has 30 minutes travel both ways and then Home Depot ran out of that special light bulb.. 

You will use conventional or FHA, but it's VERY hard to win in Northern NJ with an FHA loan on a multi just because most sellers interpret FHA as not having the money instead of an investment vehicle so that needs to be explained.You aren't going to learn much in an online underwriting course as most of those are for commercial properties and no one online can teach you how to underwrite a small multi in Northern NJ because the vacancy, cap ex, taxes, are all different.

Would a SD401K, SDIRA, or SDHSA work as an asset protection vehicle?

you looking for a vehicle to reinvest it or just wire from bank to bank?

Here in Charleston, in order to apply for the legal residence tax assessment ratio, all owners have to provide copies of tax returns, utility bills, driver licenses, vehicle registration, voter registration, and the settlement statement/CD, along with an affidavit stating that all owners occupy the residence and do not claim legal residence anywhere else.

The lender will probably also want you to have an LLC as the purchase vehicle for this.