From what I understand Musk sees/saw Tesla as a vehicle (no pun intended) to fund his real purpose, that being "working towards becoming a multi-planetary species". Whether you consider this to be a sensible or achievable goal is not really relevant but it does seem to be his driving goal. From what I gather in older interviews with him and people around him he was involved in the design of the Tesla Roadster and model S as well as in the design of the Falcon 1. It is difficult to find, let alone put any trust in objective material concerning Musk since he's been designated undesirable #2 (and more recently #1) by those who see him as the one who opened up what they considered to be their playground - Twitter - to the 'deplorables' and 'bitter clingers'. This, by the way, is another reason to compare him to Edison who also had and has a polarising effect with some people seeing him as a true innovator while others see him as an egotistical businessman who was intent on stealing others' credit for personal profit and who wielded patents as weapons to keep out superior competition in the form of (Nikolai Tesla's) AC power networks.