#5 is a killer for so many places, maybe the most common big mistake. This is one place where "fake it till you make it" is absolutely mandatory for success. Selling yourself as a "freelancer" devalues everything you do. Selling yourself as a startup is similarly dangerous. Having the cutesy small business/startup vibe might sound appealing to customers and the valley but it makes you look disorganized and unstable to big successful businesses. These are the very customers willing and able to throw lots of money around.
I cringed at GitLab's unnecessary transparency recently because it makes their vulnerability and management missteps all more apparent. Their mistake is the kind of shit where the better choice from a business perspective is to be reasonably honest then give all your customers a free month or two so they stop talking about it. Their absolutely transparency exposes a lot of internal politics and missteps, especially mentioning people by name, A HUGE no-no in any kind of big business. If I was fortune 500, hell even INC 500, I would run away as fast as possible.