I'm a big fan of the open source ethos. From a philosophical perspective, there are some things that deserve to be open source for the benefit of the community. From a practical perspective, if you don't know your main customer, going open source can open you up to the largest base of customers and allow the customers to help you find your demand.
I'm a big fan of finding the least path of resistance for the short term goal. When you are a small startup, you need to find the path that gives you the most traction, quickly. You do not want to fights wars that you don't want to fight (not efficient, waste of resources) nor can fight to win (you are small, the competitors are big). You want find allies that are also small so that you can all go down the journey of least path of resistance together.
I'm a big fan of finding the most direct path to the long term goal. The least path of resistance is not always the most direct path to that goal; sometimes that's ok, but oftentimes it's not because it's inefficient behavior. Why build 5 steps when 2 steps will do?