I think I have NSD figured out but I have one minor question ...

How will other name servers around the world know to look at my DNS for the hosts it controls?

Currently with my registrar, I instruct them to take a gander at ns{1,2,3,4}.linode.com for my registered domains. The idea is to run my own and remove the entries from linode's dns manager.

If I change that to ns{1,2}.mydomain.tld - I don't think it is going to be able to find it.

Do I need to specify IP for ns{1,2}.mydomain.tld ?? That would work, but seems less robust, as I would have to update the record with the registrar should I move it (which I suppose isn't really that big of a deal)

I know for additional domains I manage, as long ns{1,2}.mydomain resolves it should be able to find it by ns{1,2}.mydomain.tld but what about for mydomain.tld itself?

I can't be the first to wonder about this, but I don't seem to be able to find an answer on google.

At your registrar there will be an option to create name servers where you can specify your ip and the hostname. If you don't see an option ask your registrar where it is, not all support this.

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Something others here do is to leave it as the linode DNS servers and set them as secondary to your primary (if you need the level of control of running your own). That allows you to just run yours with control, not have to run a second, and have the redundancy/geographically dispersed linode DNS servers.