Essentially, the cap rate is the proportion of Net Operating Income (NOI) to the property's value or selling price:Cap Rate = Net Operating Income (NOI)/Property ValueThis ratio offers a direct method to evaluate the yield a property generates in relation to its cost.For advanced real estate investors, integrating additional factors might prove beneficial:Vacancy rate: The duration the property remains vacant.Operating expenses percentage: Includes insurance, utilities, and maintenance costs (excludes mortgage payments, depreciation, or income taxes).The adjusted formula for net income, incorporating these considerations, is:Net Income=(100 − Operating Expenses %) ×(100 − Vacancy Rate %) × Gross Income

Depending on the market you're interested in your looking at a mil++ for a 4-plex.

A strong valuation and even pre listing appraisal and/or inspection can sometimes be a worthwhile investment but not a necessity. 3-5% commission for what is effectively commercial property is common. 

Is your DSCR ratio greater than 1-meaning are you cash flowing (according to the lender's criteria of mortgage, property taxes and insurance (and HOA) if applicable).

While mortgage+ taxes may be similar to rent, you are not paying down the principal early on in the mortgage and closing costs on either end are likely to add up. 

Transaction costs of selling, then buying will mean a hit to the equity that you have, plus a likely tax hit.

so If it rents for $3,000 I take 30% of that out for taxes, insurance, maintenance, etc. 

My current primary ( scenario 1) Keep the primary for the life of the loan ( current rate is 4.5 so i dont see my self refinancing anytime soon)current home value 1,150,000Loan amount 935,000appreciation estimate 5% per year after a 28 year hold and the house is paid off I would have a house worth 4,312,000$my current mortgage is 6125$ ( piti) included My second option( scenario 2) Sell the house, walk away with $150 ,000 ish in hand and put that into a low cost index fund Rent a house elsewhere for about 3000$ ish and take the extra 3000$ im saving everymonths from not having to pay my mortgage and puting that money in the index fund as well I ran the numbers on both of these scenarios and doing what I mentioned above would break even at about 28 years meaning my stock account would be worth 4.3 million just like my house would , but the only is that holding a house for 28 year would mean 28 years of property taxes, loan interest ,home insurance and repairs etc whick I calculated to be about 1,200,000$ at minimum which raised my eyebrows to say the least Also i understand that each of these options ( stock market vs real estate ) will have there tax consequences ( long term capital gains) so any thoughts on that would be appreciated as well.  

But it you really want new financing you  should look into either a standard fannie/freddie investor loan or a DSCR loan depending on your situation

In researching this, it appears that the auto-conversion may be on a bank-by-bank basis, and would depend on the HELOC product you have chosen.