Thanks Mike,
As an interim update (I've been working on more pressing tasks on this particular client site) I've decided to firstly try out a free plugin to begin with, whilst perhaps suggesting the WPschema.com (Brainstorm Force) plugin you suggested seems pretty good. I thought I'd see if there was a free version, but perhaps even more useful than that is the free Schema course which I might enrol into next.
So the plugin I've hastily opted to try out (based on a recommendation from an article, 4.5 star in the WP plugin repo. and as it was updated a week ago - better than 3+ months like some of the alternatives) is:
I thought I'd share the first plugin in case you spot that it is not a good choice, but now I've found the Brainstorm Force plugin in the repo, I might have a think and actually try that one first instead.
I plan to post at least another update to let you know how I get on with it now I've dedicated some time to learn & work on schema.
In other news (totally unrelated but affecting my pace with WP work) I've now finally landed a full-time job, offering the structure and financial security I kind of needed to for longer term security and happiness. I'll be able to finally set time aside to work on personal WP and other projects (or maybe gaming & photography) :)
Take care,
Andreas