Deeper explanation of my BRRRR project

[Noah Bussanich]

I found a property that I am really considering purchasing. It would be a 500k purchase, 100k rehab and 700k ARV. I would then turn it into a rental.
1- First off, I am having a hard time wrapping my head around the fact that refinancing out of the loan amount would make my mortgage higher. What is the point of refinancing out to a higher amount for a higher mortgage if original purchase price has a lower mortgage? (plus higher property taxes due to the new assessed amount)

2- I don't have cash for the rehab yet, so any advice on going about sourcing the 100k? or should I ask for a 600k loan and lay out my plan to my mortgage  broker?