For automated testing, it really depends. I think it starts around zero and then ramps up over time, usually whenever you hit a situation where you actually feel the pain of not having enough tests, it's a sign that adding more would be good.
As for focusing on best practices and patterns, any more than 5% of your energy is a waste of effort. Have a reasonable set of defaults, tweak it over time, and only worry when it hurts.
(These are again, things that are just based on my own experience/feelings. Keeping w. the theme of the post)
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