Hello Ben
As a guitar maker repairer about to retire after 45 years I can hopefully give you a few tips.
1. Learn to make guitars the old way by hand and with routers chisels hammers etc first , It's no use getting a cnc machine to do everything if you don't know how the final guitar should be.
2. Figure out how big a guitar you are going to make. This is vital so that you can size your machine properly. Obviously if your making Les pauls or strats your going to need a smaller machine than if your making big Jazz guitars.
I'm using an early version of one of these
https://www.ebay.de/itm/CNC-Frasmasc...0AAOSwUKxYckYX

with acme threads it works just about and is reasonably accurate cutting but a bit slow and resonates a bit at some. (I would imagine the newer versions with ball screws would work better)

It's important that any machine you get has a high enough z axis as if your using cutters with a 50mm cutting edge to be able to do a finishing pass around a lespaul body which is about 50 mm at the edges. any cutter with that length of cut is going to have to be quite long so the retraction height is going to have to be reasonably high (my machine is about 125 mm which is a bit short) the problem is, is that some of the manufacturers give the z axis dimension without a spoil board and you'll lose some of your z height with the spoil board.

I would recommend a machine with a 2.2kw spindle motor if possible (I use a Kress FM1500 router which is accurate but noisy and only takes up to a 10mm cutter shank)

I am in the process of putting together one of these https://www.sorotec.de/shop/Portalfr...Line-0805.html
They are a bit pricey but the parts that I got seem to be ok only time will tell when I get around to putting the thing together.

Jazz can probably put you right as to whats available in the uk.

A very important part of getting into cnc machining is that you are going to have to learn the software for the cad design which is quite a steep learning curve (or at least it is for an oldie like me) I bought some guitar plans form various internet dealers in 3d guitar cnc plans which can be adapted to your own requirements to save time.
Don't expect your cnc machine to do everything there's still a lot of handwork involved in making guitars. It is quite satisfying to see a pearl logo being cut out without rough edges and filing to clean, although I could cut it with piercing saw much quicker by hand but wouldn't want to do 5 at a time.

Buying a cnc machine is quite an investment so don't rush it and try and make a list of your requirements. When I bought my machine I had a mad urge to buy one had some spare cash to write off against tax. I bought the thing and had it sitting for about 10 years in the corner of my small workshop because the noises it made when I started it up frightened the life out of me the motor would ride of merrily into the end stops which didn't, the software supplied with the machine was in French/German /English all at the same time. I gave up with it. Only when I bought a UC100 adapter did the machine seem to do what I told it to and so I slowly got into using the machine. I think it's a lot easier these days with you tube and the internet with plenty of instuctional videos. One thing having a cnc machine is that it's not shake and bake but once you have it up and running it can do a lot of difficult tasks without having to make up jigs and can also get you out of trouble doing guitar repairs to. I hope some of this helps. If you have got any other questions feel free to ask.

Cheers
Andrew