Just order a 6040, thinking about upgrades and need advice

Hi all, I have done a lot of research on these machines prior to making my purchase and have come up with a rough plan for what I would like to do with mine. My end goal is to use it to cut harder aluminum alloys and I am looking to get as clean of a result as possible. Ultimately what I am looking to come away with is something similar to this: https://www.ebay.com/itm/CNC-6040-4a...gAAOSw4nVfZA3Y

I picked up the beige 6040, 1.5kw, 4 axis machine and got it for an extremely good price due to it throwing an error and not moving. I did this because from my research I had seen a fairly common view that the electronics in this machine were unreliable, especially when wanting to accomplish what I was trying to do. Since there is some ignorance on my part about what all I will need to accomplish my objective I was hoping some of you could help me fill in some of the blanks.

Immediate plans:
Since the machine is essentially non functional at the moment my plan was to first redo the electronics and cables completely. I am nearly 100% certain I will be going with a UC400eth or UC300eth and UCCNC, so that would probably be the first question I would like help with, which one (300 or 400?).
I would like to replace the cables for the steppers and spindle, I had seen some people discuss shielded microphone cables? Any suggestions on cabling replacements would be appreciated.
What other electronics within the control box may need replacement? Breakout boards? Since I got this machine very cheap I dont mind spending a bit on upgrading existing components even if they might not be *bad* per se.
Steppers?

So my initial goal is replace some (most) of the electronics and simply get the machine operating. Once I have the machine operating and I get comfortable with it then I would like to begin my second phase of upgrades.

The next wave of upgrades would center around improving rigidity, upgrading spindle, and bells and whistles.
I would like to upgrade all 3 axis to supported linear rails. I would need information on the differences or what to look for in these.
Upgrade of the ball screws (if needed)
I am going to have a 3/8-1/2" steel bed machined to replace the multi part aluminum bed and add weight/strength as well as provide more convenient work mounting.
Upgrade to a 2.2kw (3.5?) spindle, mostly for the larger collet size. Any suggestions on spindle/vfd would be greatly appreciated. I noticed most were similar to the one that comes with the machine and would likely need a larger mount to replace the existing one. But I did see some that appeared to be square and mount directly to the Z axis, would that be preferable?
Upgrade the gantry to reduce deflection and help support the extra weight of the spindle upgrade.
Potentially replace the Z axis. I am hoping I would just be able to upgrade it to linear rails and it would be fine, but I am not even sure what that process would entail for certain. Again I just ordered it and I will be able to answer some of the questions myself I believe once I can get my hands on it, im just anxious to start planning and appreciate all the experience the members here have.
I believe with those upgrades I should be able to get my machine about as rigid as one could expect for one of these, but any other options would be greatly appreciated!

Less importantly I would like to install limit switches, z axis probe, and air/fluid sprayer system as well as a splash pan under the bed to collect liquid/chips. This is where I am wondering if the uc400eth vs uc300eth comes into play? Is the 300 the better choice for adding the additional stuff like the switches and probe etc? Any suggestions on limit switches or probes?

I will continue to read through the forum and try to answer these questions myself, but I wanted one place with all my questions to make it a little easier to track. Machine arrives a week from tomorrow and I was hoping to order my UCCNC controller and cables asap so I can get working on it right away. Like I said, step one is just getting it up and running with the new controller/electronics. The rest of the stuff I will likely make my decisions and purchase everything I need before tearing it down and putting it all back together how I want. Thanks in advance for any help!