You should definitely know about LSTP thin clients.

You should be able to setup some basic servers.

You need to know some equivalent Linux software for what companies are using. Also it would be good to know how to use them.

I'd say that programming isn't necessary, but some shell scripting is.

You need to know what is allowed with the software licences like GPL, MIT, BSD, ... and could also help to know what Windows licence does not allow, if you are going to defend open source solutions.

But, being the sick sad world that it is, to be a consultant the only requirement is to find someone to pay your bills.

I am not a consultant myself, but these characteristics sound fine:
- knowledge in very wide variety of topics.
- some basic programing skills in different languages.
- reading, reading, reading.
- catching up with tech news hour by hour.
- having an adventurous spirit to try and experiment new stuff.
- good knowledge about web servers, databases, security, networking, etc..

Get a Red Hat Certified Technician Certificated by taking Exam

You can add two items to your list: Networking skills and a reputation.

To increase your potential client base, networking skills will be a true asset! And if you're having difficulty finding paid work, you might look to do some consulting for churches or non-profit organisations, or working on open-source projects. Once you start building a reputation, jobs can appear in a type of snowball effect.

I see that lots of diffrent Linux User Roles are shuffed up to one consutancy role. AKA Linux Guru.

A PHP programmer does not have to know "advanced" networking skills (DNS setup/SElinux /Mail servers) Nor advanced license issues. Basic GPL vs LGPL understanding is totally different than being a legal consult.
But there is a very strict basic requirement rule.
If you want to start a company a clear basic scoop has to be met a Certificated an Exam surly will do the trick.