When is it optimal to include other people in a startup (including a co-founder)? Currently, I've talked to people about the project to validate the idea however I have this thought that it makes more sense to wait till version 1 is complete and the startup has at least achieved lift-off to have other people join in. Or is it better to have someone working on the project during version 1 and at launch?
Having tried to do businesses on my own, and with a co-founder, I would recommend:
You want a co-founder. You will get to 'lift-off' much faster with a GOOD co-founder. It's sort of like marriage: married people are statistically happier (businesses with co-founders are statistically more likely to succeed). I would bet the one with the right spouse are much happier, and the ones with the wrong spouse are unhappy.
Actively working on the project while you look for people will allow you to get results during the 'dating' period, and will also impress good potential co-founders.