point 1 is rubbish as usual, Look if you can build it then build it and get some investment and hire the talent you need. If there is no co-founder to be found that you don't have a long history with someone that fits the bill then go your own way. If you fall out with a co-founder after working all those long hours then you are screwed.
I like the 2 insights:
-You need a cofounder that can build it.
-You need a cofounder that can sell it.<p>These are not necessarily mutually exclusive skills, but there is rarely time to do both as well as you need to.