The best strategy is to focus on properties that cash flow at today’s rates and consider a refinance down the line as a bonus rather than a necessity.

Bonus Tip: If this quadruplex is out of state, I’d highly recommend building a reliable local team (cleaners, handymen, etc.) and maybe consider hiring a co-host or VA to help with day-to-day tasks, especially if you scale up. 

Quote from @Samuel Kim: Hello i am a doctor who wants to use cost segregation/bonus depreciation on my 9 rental houses, my home maker wife wants to meet the 750hr test to obtain real estate professional status and material participation.

@Drake BackmanBigger Pockets is a great place to find a tax strategist specializing in real estate taxation.A good real estate tax strategist can save you thousands of dollars by leveraging entity selection and formation, tax deductions, cost segregations, bonus depreciation and tax planning.I recommend finding a tax  strategist specializing in real estate taxation, business taxation, financial planning and tax planning.Consider working with your tax strategist remotely to expand your options.I would also recommend looking for a tax strategist willing to work with you throughout the year.

Bonus points if I can incorporate technology to streamline applications.

I'd recommend speaking with local specialists in your target market to look at multiple investment options side-to-side.Lastly, some of my clients have been encouraged to stay away from HELOCs unless they expect a lump sum (inheritance, sale of other asset, bonus, etc.) to pay off the HELOC in the next year or 2. 

for me, the ones that cashflow the most are the ones that I bought with 3% long term debt, they were new (low maintenance) and they are in high appreciating areas(just a bonus but does not impact cashflow).

Yes they are a nice bonus, but you could find yourself on the end of a lawsuit due to a guest getting injured or even killed.

More work, more time but you can take advantage of a nice cost segregation / bonus depreciationThis is the truth! 

Remember, investing 200,000 into an ADU won't likely increase your properties value by 200,000, but the rent potential is a great bonus.