The problem with the water cooled 0.8-2.2kW spindle is they lack torque at low speeds, so much so that if you need to machine steel you'll be limited to very small (3mm or so) carbide cutters. You get roughly full power down to half speed, then it drops linearly to zero at zero rpm from there. That does mean for aluminium with cutters up to about 8mm they're excellent as that's within the roughly full power region.

It's difficult to find a spindle that will cover a good range of speeds, so the best way in my opinion is to make your own using a brushless motor or incorporate pulleys. www.hobbyking.com has plenty of good ones to choose from

I doubt putting a 2.2kW motor is a safety concern and due to the above you've not really got much choice. I've just stuck a 6kW motor on a C1 lathe...