I won’t question why you are using the X2 spindle and will assume you will be happy enough with rpm’s as you have been using it already.
As for the Z axis; only you will know what a suitable height is. This will need to be worked out from cutter lengths, material thicknesses + jig height and clamping methods. I would recommend you having a good think about what is likely to be your highest setup and workout how much clearance you will need on the Y axis. It might be a good idea to add some extra for just in case situations. Obviously the lower you can keep it the better so keeping the jig base height to a minimum would make a difference to Z and Y axes rigidity.