All HELOC rates are adjustable (usually adjust with prime) unless you go with a bank that offers to lock the rate for a HELOC draw (usually for a fee) and banks that offer these usually have higher initial rates also. 

I made sure I kept six months mortgage for vacancy and any initial rehab/maintenance.

Only one of our properties has any of our initial investment still in it (it was purchased NYE and is not a BRRRR). 

They initially said no, but after some negotiation (4 months) we settled on the sale price.

I made the initial walk with a GC and have his quote but am looking to see if I can run some options to stay on or under budget!

After I purchase a property cash (for it's initial advantages), what is the best way to finance it in order to get my ROE right and more so my cash back for further investment?

After I purchase a property cash (for it's initial advantages), what is the best way to finance it in order to get my ROE right and more so my cash back for further investment?

However if there are no descendants or lien holders to initiate probate proceedings, is it possible for an interested third party such as myself to do so?

I was initially thinking one of the light gray vinyl plank choices, but wondering if that would clash with the existing flooring at the transition (by the breakfast bar in the photos) Any advice would be appreciated!

Considering that they should be out and are basically pulling a fast one on you (POA's should be negotiated during the initial contract signing, not after closing), I would charge the very upper end of market rent and demand a large security deposit.