Would love any additional info and the chance to check it out! 

NEVER borrow from a 401K, you are taking pre-taxed dollars and paying it back with after tax dollars, you do not get to return the loan with pre taxed dollars, in addition, some 401K plans do charge interest and maybe even fees, and lastly if you get laid off for some reason, it is a distribution with all the "fun consequences: tax at the last dollar rate, and if you are under 59.5 there is also the additional 10% penalty.Personally I like the HELOC, however you can also sell stocks and do tax harvesting there to offset gains if that is an option

Additionally, involve a real estate attorney to ensure the transaction aligns with legal requirements and protects both parties’ interests.

If the water bill is $100 a month, increase the price by 20% (or whatever you decide is fair) to compensate you for the time required to split and bill and to cover additional use when tenants squander the utility.

Verify if there are additional adults or other violations.

Also, you will have additional occupancy tax depending whether you are in the city limits or not.

When it comes to housing, the FHA rules apply in addition to those of your state/city.

If your wife and kids aren't moving in with you, then it's not your primary.

Additionally, they've avoided 40-50 hard credit inquiries populating on their credit as a result of the soft credit inquiry that we utilize for DSCR loans.If DSCR loans are a new thing to you, I would recommend checking out some articles here on Bigger Pockets or giving me a call to learn more.

Duplex have different zoning that may permit additional units.