have the cncest 6040 1.5kw spindle with the bsmceo4u-pp usb controller board.

BACKGROUND - YOU CAN SKIP THIS PART:
I've cut a boot for dust collection, did some cup holders with engraving, did a number of other projects and it's fine. I mostly bought a cnc to do guitars and started doing one and it cut the body shape fine, cut my pickup cavity, but then the neck cavity and full stop. I've been troubleshooting this quite a bit over the last few weeks and just ready to feel like I'm moving fwd. have tested my file with camotics, written files to test accuracy, tightened the couplers and support bearings, calibrated the machine, built a new pc for it and have made zero progress. If I run many programs I have with complex curves... they run fine... but the very fine details of a slight tapered neck pocket cause this thing to find a new x that is out by a LOT after a short time. Have had help from a few folks here and several on other forums... and am exhausted by it at this point.

so... at this point considering getting a g540 as I know so many here have had great luck with them. I really don't want to use anything from the current controller as worst case scenario I can go back to it. I have ordered replacement wires/connectors for the steppers and vfd and will replace those first either way. should that not solve the issues g540 is my next resort.

option 1 is (pre built gecko g540 + a vfd):
https://www.ebay.com/itm/Gecko-CNC-G...G/264943072064
+
https://www.ebay.com/itm/1-5KW-VFD-S...t/202241904211


option 2 is (buying a kit from homann - my budget is about $600):
https://www.homanndesigns.com/pdfs/EN010_V8.pdf


either would require this pci parallel card:
https://www.amazon.com/gp/product/B0...SW0DLDLX&psc=1



Q1: so... if I understand correctly I could get option 1 and this should get me to the point where I have axis movement pretty quick... then the vfd... is it as simple as 3 wires to the vfd, 3 power wires, and go (for manual control)?

I've got experience wiring some fairly complex guitar items... following schems, creating my own pcb, troublshooting... but I am admittedly out of my element afa troublshooting a controller should it come to that. I know the homann would seem like a better supported option should I venture to try and get mach3 control of the vfd.
Q2: I don't understand what the "CN-02 Auxiliary relay output" is for?
Q3: is the female IEC for the vfd for water cooling? this option also has the inclusion of a fan... which I'm guessing is going to become critical for me as AZ garages reg hit 110+ in the summer.
layout diagram seems fairly easy to follow... famous last words!
Q4: I assume I could simplify this wire up by just leaving my water cooler running as I do now?

I have read quite a few threads on this forum to try to get past this... but if you've got another one I should read I'm all ears.

any/all advice welcome.