I am a new CNC user. Here are a few thoughts about my experiences with the eShapeoko. They are much more relevant to a new user, since old hands will be well aware of them already. But people new to the field may not have thought of them yet...
1 - The kit is a mechanical kit, and so you will need to buy the electronics and motors before you can have a working CNC machine. But what is just as important is that you will need an underlying structure to build on. You really need to arrange this first, otherwise you will be trying to build a structure with nothing to support it!
You will need a suitable ventilated container for the electronics. You will probably need connecting plugs, which will make it easier to assemble sub-systems separately rather than working in a forest of hard-wired components. Most importantly, you will need a firm, reasonably flat base board to assemble the eShapeoko framework onto. Without this you will find it very hard to keep the framework truly aligned as you build it. I used extra countersunk bolts to attach the framework to the base board - these will need buying as well. So there is going to be quite a lot of essential support kit needed BEFORE the mechanical kit arrives...
2 - Tools are needed for levelling. I used a tape measure, a long metal straight edge, digital callipers, set squares, a dial indicator and a height probe. You may need to shim a few parts - I used a sheet of paper. And when you are happy with the set-up, blue Loctite is a good idea - particularly for motor and pulley wheel mounts.
3 - Once the machine is assembled, you will want to operate it. You will need some software. I used GCodeSender for Windows. It's worth downloading whatever software you expect to use, and practising with it. If you are totally new, you will need a drawing package, and a way of converting that drawing into G Code as well.
4 - You will need a cutting tool and a motor for it. What you get will depend greatly on what material you want to cut. Don't be to ambitious at first. I an still learning about this, so I have little advice I can give, beyond noting that the machine is designed for a 'Dremel Clone'. I still need to find a good source of cutting bits. Note that, depending on what you cut, you will probably need a way of vacuuming up the dust...
5 - Work Holding. This is critically important for a successful job, and you can't run a cut without it. You need a waste board on top of the base board, and some way to firmly clamp the object you are cutting. How you do it will depend on what you are cutting, but you need to plan for it rather than wait until you are about to run your first job...