You received good advice from @Greg Dickerson and @Danny Randazzo to unlock the equity in your two properties.The best way to get that next 4-unit is to house-hack it and get an FHA loan for 3.5% down.

Possibly, but it's very hard to guarantee, especially in the tight timeframe of a 45-day exchange window.If it were me, I'd wait for a while, but I might refinance to unlock some of that equity and help get another rental in the same price range (the 3rd and 4th Rs in BRRRR).

Not sure if one should lock all vacant doors and unlock once leased but this would prevent the hands off management approach as I seek. 

For example, Jan - A1, A2 - purchased these two houses the first monthFeb - B1, B2 - purchased / A1, A2 rehabMar - C1, C2 - purchased / B1, B2 rehab / A1, A2 ready to rentApr - D1, D2 - purchased / C1, C1 rehab / B1, B2 in rehab / A1, A2 rentedMay - E1, E2 - purchased / D1, D2 rehab / C1, C2 in rehab / B1, B2 rented / A1, A2 refi done, "seasoning lockup / countdown" beginsJun - F1, F2 - purchased / E1, E2 rehab / D1, D2 in rehab / C1, C2 rented / B1, B2 refi done / A1, A2 cash flow, wait for countdown to expireJul ===> ad infinitum ... repeat, using the "unlocked" money from prior generations to fund future deals.Then again, I could be totally misunderstanding what he said. :) lol

Started with savings (we'd been saving like mad for a few years), figured out how to unlock my retirement dollars, mostly BRRRR with a little turnkey and flipping in there. 

Give legal notice then knock before you unlock the door.

Benefits of using bridge loansunlocks buyers: unlocks buyers who may not have the funding on their ownpurchasing power: provides liquidity to those whose money is tied up in equityspeed: eliminates sale contingencysecurity: eliminates the fear of not knowing where your client may live if they don't sell their current home fast enoughcontrol: allows the client to sell on their own terms, while they're comfortable in their new home (for up to 6 months)I'm asking my realtor right now of what if I'm not selling my house in that 6 months time frame?

Will usually come with a lower purchase price and will allow you to unlock equity you can use should you wish to scale faster.3) Echoing above advice, I think BRRRR is a great strategy and multi-family properties provide a perfect place to employ it.

You do a cash out refi on your home and now you’ve unlocked 300-400k to park in an investment property, or multiple deals.

She understands how to use credit cards and the doors she can unlock is unlimited.