Hey Chris,
please use the search function of the forum.
You will find a lot of information, including that I have reported what I have paid here. You may also find this and this.
A spindle is a three-phase induction motor which requires to be driven by a VFD which should be enclosed into a control cabinet, for two reasons: Firstly, a VFD (and the spindle cable) is the source of heavy EMI, and secondly, in addition to the VFD itself, you need a number of other components which are conveniently installed together with the VFD in a control box that is grounded and therefore acts as a faraday cage to shield the EMI. If you want to have information on how to build an appropriate control cabinet and what to put in it, see here.
Note that Mechatron has a Web Shop for end users and even an Ebay shop.
Note that there are a lot of spindle manufacturers in Germany, Mechatron is only one of them. It is however one that also adresses to consumers and hobbyists. If you are interested in German and European spindles, see here.
If you use the search function, you will also find that there is a disadvantage in using a 65 mm spindle, because it does not clear the stepper on the Onefinity, as explained here and here. Better buy the optional 80 mm spindle mount with the Onefinity for this reason.
Welcome to the forum!