Hey David,
I think it is worth it to buy the 80 mm spindle mount and to use a 80 mm spindle. 65 mm spindles on the Z-16 Z assembly do not clear the stepper but will bump with their end against the stepper cage, limiting the Z travel unless you slide the spindle much downwards in the mount, which will increase leverage forces and thus the danger of chatter. Also a 65 mm spindle will provide less mechanical power than a 80 mm spindle, with the same electrical power. And finally, with a 80 mm spindle, you can choose whether to buy a spindle for ER 16 collets or ER 20 collets, which will allow the use of collets for bit shanks of 1–13 mm (which includes the use of a collet for a 1/2" = 12.7 mm bit shank). See also here for considerations on choosing ER size.
There are many reports of Original X-35 Y-35 with 3rd “stiffy” Onefinity machines handling the weight of a 2.2 kW 220 V 80 mm water-cooled spindle which will weigh about 5–6 kg. For milling wood, a spindle with two magnetic poles that can do at least 24 000 rpm at 400 Hz as max. rating is recommended, as milling wood requires both high speed and high torque.
Regarding the VFD, often people buy the Huanyang HY Series without knowing that they don’t support Sensorless Vector Control (SVC), which I would recommend to have on your VFD to make the full benefit of a spindle’s capability. The VFD PwnCNC sells (VFD Manual) has this capability.
I could recommend what I bought, but this will not correspond to the criteria you wrote above, because I bought industrial quality with the german spindle at about €1000 and the japanese brand VFD at about €400. I can tell you what I bought if you like to hear though.
You may read this for further information:
- A question on spindles – Post #4 by Aiph5u