ok, saying PM will fix it is cheap but that's really the core task of project management "to devise a plan"
But a specific plan with goals needs to be based on an analysis of the environment you are actually in and you did the first steps, you tried to describe the environment.
medium-sized enterprise, UK
Ok, you're in the UK and have access to a solid workers pool of skilled IT, also available by contract workers.
Think about getting an aide, nothing is worse than a project manager that looses oversight!
They claimed to be an advocate of open-source.
But everything contradicts that, don't cling onto open source, don't waste energy to educate people that don't understand. It's useless, and open source is only one solution, that can work but also can fail. Especially if you have people with no skill!
The job was advertised as a Linux sys-admin. I've been in the role a short while and the systems right across the business are end-of-life: lots of XP and 2003 servers, a handful of LAMP web servers,
Do you have an overview, are all the systems accounted and cataloged with "Machine Power"/"Electric Power"/IP/MAC/Remoteinstall/config etc.. possiblities.
Because this actually looks like those who hired you did not have such an oversight.
and a large IT department with almost no skills in the technologies on site.
First you don't need a training plan you need a Maintainance&FIXIT plan = nothing is worse than systems failling, when you grab resources for training. because you will be blamed for, your oppinion will lose worth you will lose resources.
Idea: Have a fix-it task force at hand. Only selected few who really can "fix it".
(Think about high skilled contract workers.)
Most boxes have the default password still.
That could be getting fixed by a task force.
As a senior techie, I've been tasked with helping bring the skillset of the rest of the staff up.
Good luck with that.
Where would you start, given that most of the kit is EoL?
Make a plan based on the current equipment(what can still run and what is really dead) and the demand of the market. ("priorities")