[farmerdee]

I have actually written a tool to help organisations understand their own digital exposure/privacy. It is very much an MVP but check it out, it should help you with some of your concerns - https://www.privacytrail.com

I think DDR0 makes a strong point, a determined malicious actor will always find a domain you haven't considered so defensively registering dozens of domains is usually only an action taken by large banks or significant brands. Unless you are likely to be impersonated or have a duty of care similar to that of a bank then a single/small number of domains is probably sufficient, especially for a startup. Buying additional domains can be done as you get larger and the threat of impersonation increases.

However, that doesn't mean you shouldn't monitor domain purchases that are similar to your own. Blacklisting domains that you believe have been purchased for nefarious goals can prevent your own employees from being duped in convincing phishing attacks and it is always good to occasionally remind customers/third parties of the domains you operate from.

Anyway, I could waffle about this for ages - there is more info on the above link and you can try your own domain out!