This is a build vs buy question. If you need to work now you may just want to purchase a machine turn key. If you will be making money with the box, the hasle of learning how to build it is not worth the tax benefit of buying a turn key machine.
All that said I can see from the post you have a lot to learn in the drive space. You should look at the kit setups that have everything you need like a Joes CNC.
Or this machine
CNCmachines6090 from Keling
Look at my machine if you have the space. Average build time is about 6 months. But I have seen it built in a month, but that is someone who knew very well how to build a CNC Machine. It can be sized to do 4x4 work.
Keep in mind what ever you do to know what sofware these machines use and make sure it can create you cut files. (Or pay someone to make them for you to get you started).
Also if you are just prototyping you can find someone who has a machine to run a file for you .. aka jobing out the work at first.