Bit of a flood ! And a couple of questions.

[JAZZCNC]

Firstly, I have two noisy bearings and so will replace the bk/bf blocks, the ballscrews are 25mm but turned down to 15mm at the fixed end and 15mm ( threaded part ) then 12m by the coupler. So it looks like I need BK15 and BF15 blocks, is this correct ?

Yes that's correct, 15mm is the ID of the bearing and usually with M15 x 1 thread with coupler portion being 12mm OD.

While I was looking at it I thought maybe replace the ballnut as I have to take it apart quite a bit anyway but I can see no markings at all on the part and I wonder how to make sure to get the right ones regarding pitch etc.

I put a ruler on it but not sure exactly where to measure to and from.

Any ideas ?

First putting a ruler against alone won't always tell you the pitch because it could be a multistart thread. So for instance while the distance between threads is say 5mm which is what yours looks like, there could be 2 starts (threads) so this is double making it 10mm pitch. If you look at the end you'll see if there are two separate threads.

Now if you didn't have any backlash then I wouldn't go trying to swap the nut for a different one because if it's a Chinese ballscrew, which it looks like it is, then you might struggle to find one that matches and end up with more backlash.
If it's not worn then I would just strip it, clean and re-grease, if it's got a little backlash you could try fitting new balls or a couple of oversize balls to preload it a little.

Secondly, I plan to do drag chains and redo the wiring and add back in the limit switches I removed.
I would like to use some kind of connectors at either end, at the moment everything is chocolate blocks or just wired straight in.
I like the type of thing found in car connections like the deutsch connectors or that kind of thing. I know its not strictly needed but would make it easier for future maintanance is there a go to connector for this.

Aviation connectros are the most commonly used but they are fiddly things to solder and easily got wrong. I've seen many drives blown up because of poor connections shorting on the sides.
Like you say they are convinient for removing at later date or moving the machine around but they also open up a potential problem area as they get old and strained.
I fit them them on machines I build when required, for instance when access is poor and control box or machine as to be taken in separate pieces, but if I'm honest I'm not a fan and always try to avoid them if possible as it just introduces a potential problem.

Thirdly. I would really like to do a better control cabinet, its currently in a pc case and at this time my VFD is separate and not wired to the BOB which I keep meaning to do.
I had a look at this from cnc drive and thought it a pretty neat solution ( I already run UCCNC and there eth 300 controller which I like ).

Does it represent good value, (assuming I can actually get one shipped here after the stupidity of brexit )?

I am not particularly good at electronics but think I could probably do a similar setup myself but it would take me ages and I would be worried about cocking it up, unless I had very thorough instructions to follow.
Any alternatives.?

As it happens I can help you here if you want a box building and I'm just about to build the exact same thing for someone.
I now stock CNC Drive components and have both the AXBB-E and UC300 in stock along with wireless pendants and tool touch off plates.
I also stock energy chain and other components like Water cooled Spindles, Closed loop stepper sets, etc, that I fit to machines I build. I don't normally stock BK15 bearings but as it happens I do have a couple of sets that I ordered for a job but never used so can help you out there as well.

Drop me a PM if you decide you'd rather have a box built than DIY or if you need any components I stock.