The first thing you have done right is ask.
Now the problem, you will get conflicting advice, there are a lot of Armchair Engineers on here who haven't got a clue.
They may have a fancy website have a lot of posts on here but are legends in their own minds. All the gear no idea is another description.
Anyway you don't say if you have any engineering experience or indeed any machines/equipment.
So i will assume you haven't.
So the gecko G540 i would say not so good for a mill due to its low amp/volt rating but great for a small router.
This means that you will have to use lower power motors, again OK for a router not so good for a mill. In the UK i use Motion Controlled Products motors and drivers & PS
There are limit and home switches that can and should be added
For CNC ballscrews are a must as they allow the machine to cut in the optimum direction which is called CLIMB MILLING and although you can have backlash elimination that can overcome backlash it will never be as good as no backlash and you can't move in the optimum direction.
To convert the mill you could need the use of a lathe and a mill, now if the mill is the only one you have then you may have to keep assembling/dissembling it as you go. Especially machining the ballscrews.
This can take considerable time "Think Months" and if your not experienced then there will be a lot of mistakes made along the way before getting it CNCed.
Then after you have got it CNCed then there is the software to learn, i would heartily recommend Mach3
Then to design 3D parts you may need CadCam software this can and does cost thousands. I use OneCNC CadCam this is very easy to use but is expensive others are cheaper full of bugs and hard to use.
So this may seem very negative but i am being realistic it can be extremely frustrating at times but it can also be very rewarding. You could get a ready built CNC mill but my own experience of the RF31 is anything to go by it may still need work to get it to a high enough standard. One very important thing many miss, is a one shot lube system as this will stop the machine wearing out too soon.
If at the end of the day you just want a bracket made get someone else to do it. You will get it far cheaper and quicker.
Now i have CNCed a Mill "RF31" & a lathe "M250" but i have an extensive home shop more even than WidgetMaster who is a real engineer BTW
And i know how to use it