The people I’ve encountered in my 40 + years as a real estate investor and private lender who are successful have the following in commonThey are educated as to principles of real estate; real estate law; and real estate financeThey LEARN something new about real estate investing almost every day, and are open to realigning their strategy, tactics, and portfolio to encompass new information and knowledgeThey SPECIALIZE either in a strategy, property type or geographical area, and become EXPERT in that areaThey have survived real estate “depressions” where property prices have dropped 20% - 50%They understand the difference between real estate investing, operating a real estate BUSINESS, and having a real estate job.They network, for knowledge, capital and most importantly DEAL FLOWThe key thing to consider when you watch a YouTube video, take an “introductory” seminar, or read a guru’s website, is what is the subject persons BIAS?  

Do not over-extend yourself and risk taking a large principle loss.With all of that said, a househack gives you more control than most other options.

Potential properties should have a complete financial study done to make sure they meet your investment objectives.

A careful present value of the two strategies would need to be made based upon a specific investor's circumstances, goals and objectives to determine which would be best for them.  

It may be helpful to consult with a lender or real estate professional to discuss your options and develop a plan that aligns with your objectives.

 I am also looking at the HELOC as a 1st and use the principles proclaimed in the Replace Your Mortgage pitch which I understand to be, Use it as a checking account and putting all your income into the HELOC and then pay bills from that account thereby using all income to more quickly reduce the interest. 

Am I going to have a first position lien on the property and you'll pay me essentially a mortgage payment at 10% interest so each month I get principle plus interest?  

This subject (ADUs) is discussed here often....they are the newer shiny object in the room and everyone is excited about them. 

When you price out the Principle interest taxes insurance and any HOA the rents in most states won't cover the payment unless you have BIG down payment or equity. 

just use homes.com and the AVM from 4 appraisal company usually has 1 standard deviation with zEstimate is in the middle.The accuracy really depends on the object property location and the sample.