What is Ideal Number of Keyword in a Video Title?

In the 71st episode of Semantic Mastery’s weekly Hump Day Hangouts, a viewer asked about the ideal number of keywords to be added in a video title.

The exact question was:

Hi guys, I know you go after 1 keyword per video, with your video title do you put the brand name in there too?
say, plumbers in dallas | bobs plumbing – or do you have just the keyword? Same for the meta tag of a web page.

Just one quick yes or no question, sorry – when you have multiple personas attached to 1 youtube channel, do you use the same tier 2 for all or does each tier 1 get its own content sources or can you do both, say, 1 brand and 2 personas, all 3 use the same tier 2 but also have other related content sources? Thanks?