The time factor is the biggest issue. Building a control box takes time, especially if you've never done it, and don't know exactly what you need. This makes the CNCRP plug and play packages very nice options for most people.I'm willing to spend a bit of time building from kits, but anything more than 40 +/- hours assembling a control system gets to be a bit too much.
But building your own control has some big advantages.
Imo, the main issue with the plug and play kit is that it's built around an Ethernet Smoothstepper, which locks you into Mach3.
While tens of thousands of people are using Mach3, it's obsolete, and has been for a while now. There are several competent Mach3 replacements available, with the Acorn being one.
Mach3 development stopped over 5 years ago, and while it works fine for most people, it has a lot of bugs, and other options perform better.
In addition to the Acorn, other options would be UCCNC, or LinuxCNC. A lot of longtime Mach3 users are migrating to UCCNC.
I don't think there's any reason for any new CNC user today to be using Mach3, when there are much better options for the same cost.
Let's forget about the Clearpaths for now.
One thing you can do is buy the plug and play Nema 23 kit, and swap out the Ethernet SmoothStepper for an Acorn or other control. You should be able to easily sell the ESS for $125 or more on Ebay. You'll also save the $175 cost of the Mach3 license.
The Acorn and software is about $470, but you'll be saving $300 by ditching Mach3.
This leaves you with a lot of the wiring already complete, but you may have to move some things around in the box.
One thing about the Acorn, is that is has a lot fewer Inputs and Outputs than the ESS, so you may not be able to connect everything back up that's in the box.
UCCNC, with a UC300ETH and a UB1 breakout board,gives you about the same amount of I/O as the ESS.
Now, if you were going to go the Clearpath route, you should look at your options.
Since Clearpaths would require building your own box, consider building your own higher performance stepper control.
You can get stepper motors for $60 each. https://www.automationtechnologiesin...-640-oz-in-55/
Stepper drives for $100 each https://www.automationtechnologiesin...-motor-driver/
https://www.automationtechnologiesin...k-is-included/
Good quality power supply. https://www.automationtechnologiesin...c-duplicate-3/
There are a lot of little things that also need to go in there, but these would be the major components, in addition to the motion control board.
Basically, for the same $1500 as the plug and play kit, you can build a Nema 34 setup for the same price that would give much better performance.
I think the Clearpaths are overkill for your application, and their cost really only makes sense when upgrading an existing stepper powered production machine.