Software Engineer @ Shopify | Software Engineering Mentor @ Springboard | Graduate Student Artificial Intelligence @ Stanford
Speaking from experience, when trying to launch a new startup company, testing your idea to know what works and what doesn't work is the most important thing. More often than not, the original idea you start off with isn't the right idea or really not what your customers may be looking for in your product. It takes a lot of time and iteration to truly learn what your customers want in a product.
Custom software is really expensive and "slow" to build and maintain and chances are that if you choose to learn what your customers like and don't like using custom software, you will burn through a lot of cash and time. It is best to reduce this cost of learning by using readily available solutions, learn from them and then when you have "cleaned up" your idea you can invest in custom software