For SSL I think there is industry consensus to push for HTTPS everywhere. There is no argument to skip it. With free lets encrypt certificates. It is not like you will spend a week implementing it, without prior experience decent developer should have it up and running in half of day.
I agree with you, maybe the advice should be “do this immediately, regardless of stage or size”
For instance:
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"Follow an onboarding / offboarding checklist"
Do this when...
- you have ten or more employees,
- you have at least ten thousand user accounts, OR
- you have at least ten thousand dollars MRR
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"Protect your application from DDoS attacks"
Do this when...
- you have publicly announced funding, put a major product launch or milestone in commercial press, or have publicized a key strategic hire
- a prolonged period of downtime (N minutes/breaking 3 or 4 nine availability) would have a materially adverse effect on your business
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"Use SSL certificates to secure people using your website"
Do this when...
- you are collecting any information from visitors to your website (logins, email addresses, phone numbers)
- you would not want the traffic from sessions browsing your website to be intercepted by third parties.
Of course, a lot of these things would be obvious, but there's a chance here to make this really accessible to the security ignorant or security illiterate.