1 Is there anyway to use a FirstNameLastName domain for registering for services without doxxing myself while still receiving the benefit of a custom domain?

Yes, either use someone else’s name or make one up.

2 What is the best structure for creating emails for services? For example I’m currently using <ServiceName>@CDexample.com but the downside of this is if someone knows your domain they can effectively figure out what services you use and this possibly could be used for osint and doxx you.

Yes but it’s unlikely. You can’t (typically) get a list of addresses from a mail server.

3 Should I use my custom domain for Banking and other financial related services?

Personal preference.

4 Is there any point to use a service like addy.io with with a single custom domain?

Personal preference.

5 If i use my custom domain on my cv would my whole domain forever be correlated with my other personal data on my cv and sold to data brokers?

Yes, but this is probably low-consequence, at least for the near future.

6 Is there any point to own more than one domain?

Yes.