Unless you live in a state where deposits have to be kept in a separate account (google) I would open 1 business account and a credit card for the rental property. 

I have a cousin in Florida that is moving and would love to come to an agreed price on their place but just take over the mortgage instead of securing my own loan as I am looking for it as an investment and would be required to do 20% down (which I would not have). 

These loan times will also require you to sign a document that states you are going to occupy them within 60 days of closing.

Due to item 1, adding an ADU can require years to start achieving any return (once the accumulated cash flow recovers the initial negative position).3) Adding an ADU is a slow process.

Most of the lenders we have spoken with such as western alliance bank and Axos will require a $25M minimum.

Are low rises exempt from the requirement?

Your either going to beat your head on the wall because of the debt and stress about it making money or stress that you paid all or a substantial amount of your cash when you go all in. i understand this will be unpopular for a lot of BP viewpoints but it worked for us, we own 2 STR that we owe nothing on now and purchased both for 670k and have a real value of $1.2-1.3mm. it requires you to put a lot of your cash back to your reserves but you have it all to do it with.Personally we believe in ourselves and our ability to pick high producing properties(that is the very first and foremost consideration) then we went all in and never looked back, 2 years later bought our second STR with mostly cash. 

Their perspectives have been invaluable in highlighting the nuanced balance between the challenges and rewards this venture entails.Self-managing, especially given the property's distance, presents unique challenges, primarily revolving around the commitment required for regular maintenance and promptly addressing tenant needs. a property management firm I'm considering offers a fee of 9.9% or an intriguing maintenance-only service at $95 per month.

They require 20% down then will finance up to 80% of the ARV.

The max LTV is not quite as high as FHA, but there is no sustainability requirement for triplexes and quads (FHA triplex and quad must meet sustainability requirements).