This method has enabled me to buy nine houses since 2011.

What would be the best method of a loan in order to secure the down payment for the new home? 

What would be the best method of a loan in order to secure the down payment for the new home?

.,.....assuming you can get at least a 90K  heloc - you can then  use  whatever amount of advances  you need   for  * down payment on rental * rehabbing  etc even though the heloc rate will be higher than the rate you can get on a cash out refinance - the outstanding balance that will be on the heloc  is realtively small  and thus  this rate  concern isn't that large

@JohnPaul PachecoYour question leaves me a little concerned that you don't really have the knowledge to go into this an be protected.  

I am not planning to buy a 100 homes a year, just to methodically buy (cash) and sell houses using equity and my savings.     

@Peter Moser @James Myers Have either of you tried this method?

If these deals were single families I would do a reno in a heart beat because the "BRRRR" method works well with the equity game.

Any concerns of the distributed nature of the apts?

If you are still concerned, get an umbrella liability policy and/or move the property into an LLC.