Knowing the consequences of refinancing

Context: I currently own a house with a mortgage up for renewal on November 2026. My mortgage is a little under 300K but I know that my house value on the market now is closely to 709K. I want to buy another property and am trying to figure out if i should refinance my mortgage on house A to get more down payment for house B or simply go with the minimum down payment for House B (it’s a new build so I can go with minimum 5 ) my main concern here is that i do not want to be stuck with payment a mortgage of 4000$ a month on house B…. any advice would be appreciated.