@Jerry ZhangYou can also put a lien on one of your assets for a short period of time.

Agents may also have macro data on historical data, local median sale prices, absorption rate, etc to help with your analyses and projections.Networking/build a team: Attend local meetups, virtual meetups and stay active on forums like this.A lot of this will be done in front of a PC unfortunately but if you cut out the noise, you'll be able to maximize your time.Lastly, something that has helped me tremendously with respect to focus and improving efficiency is the pommodor technique. 

Is it a big hassle to add the extra money at the end of each year, or whatever the reinvestment period is?

Just making extra monthly/periodic principal payments is good enough for me :)Of course, you need to be a "saver," not a "spender." 

I happened to be the landlord and got a very favorable lease with an arbitrage operator and I'm pretty sure they lost money over the period of them arbitraging with me.

A Home Equity Loan is usually a chunk of money you get up front and start making P&I payments on right away for a set amortization period.

Apologies for all the questions but figured it'd be more efficient all in one post.

Aiming for conventional and not a DSCR loan due to costs and the higher down payment requirement for the latter.With that said, I'm curious to hear your take on what the most cost-effective & efficient approach would be to source a down payment.

Focus on multifamily properties, explore value-add opportunities, and use technology for efficiency.

There really isn't enough information here for someone to give you a proper answer.What you need to do is calculate those tax savings over the next 5-7 years (or however long you plan to stay in the house) vs. what the interest rate reduction will save you over that time period.