Thanks for the responses all; really confidence inspiring to have the support from places like this.

Some stuff for me to look up there, I think... lots of terminology. "Profile" rail, will look into what this is.

Good points raised that I haven't talked about size. Basically, nothing massive needed, I would think the largest piece of material I'd ever work on would fit within an A3, maybe even A4, footprint. I'll probably pick where it's going to live and build it to a sensible size, see if I can find a corner of the garage/workbench, or build something in the corner of the shed, but either way I think if you imagine it no bigger than say 1mx1m workable area TOPS (and I think that would be overkill), it's about the right scale.

Must admit I've been hand-cutting 3mm steel for bracketry for years now with the plasma cutter and thinking how lovely it would be to do this CNC-guided :D but I do so little of it, it doesn't warrant the construction of a piece of kit to do it. But every time I look at my wobbly-edged plasma cuts I dream of how much neater it would look :). Steadier hands instead, maybe (I'll have to lay off the coffee)....!

Thanks again all; please keep any first advice coming. In due course I'll no doubt raise a separate thread with appropriate questions. It will be some time yet I suspect; but I get an idea of something like this in my head and then I can't sleep at night with all the questions that keep bouncing around... am I being overly optimistic, is it practical, realistically achievable, will it do what I want, how expensive will it be, etc.

I don't expect you to answer those ones though.... not yet, anyway!