What you do bring in equity from investors.  

My wife and I are currently starting out real estate journey. 1.5 years ago we bought a dental practice, and last year we purchased our dental office building priced at around $2M with $500k in equity.

Even if you borrowed 400k against it now, you'd have well over 500k in equity in 10 years (500k plus the principal paydown).To me, I think you refi it and pull the money out entirely tax free.

(It was sweet deal and the (ARV) I will have about 300k in equity to tap in on)

You hope either (1) neither lender finds out and or (2) neither lender decides to take action if they find out.Second, you make up the difference in equity with either (1)cash (2) 2nd mortgage loan with the owner with less equity giving to owner with more equity and/or (3) trading something else of value, such as another property, car, RV, etc. 

I wouldn't consider it until you have at least $1 million in equity, and even then there are other ways to protect yourself.What you do need is a solid partnership agreement.

I have a $115 loan at 2.25% on a 15 year note. The home is valued around $300k. I’m tempted to do a cash out refi. I can cash out refi $100k to a 30 year at 7% but lose cash flow and break even. I want to reinvest the...

each property has 100k in equity.

If you have 200k in equity and you are cash flowing 14k per year, that is a 7% return on equity.

Some have more than $1 million in equity while others have less.4.