I am looking to set up a Geo (DX maybe) system for a Barn that we are converting into a house. It currently has tubing for 3 zone radiant system in the slab on the ground floor. I am planning on adding a 4th radiant zone for the bathrooms on the 2nd floor and then using Hydronic (radiators) for the rest of the 2nd floor. In addition, Zone 1 & 2 on the ground floor (1,260 sqft) are basically going to be used as garage/workshop space (heated to 50 degrees) Zone 3 (900 sqft/floor) which contains the 2nd floor will be the living area and heated accordingly (67-68) What sort of setup do you think would work best? Is Geo a good solution for this? Can I mix radiant floors and hydronic? Thanks in advance for the advice.

Hydronic (water source heat) and radiant (floor loops, radiators, convectors, infrared...), can mix with geo some of the time. Lower water temps will allow you to heat with loops in the floor or wall or cieling panels, but not with typical baseboards (unless you use a whole lot of them). The area where you had radiators in mind might be served by a hydronic fan coil and air handler that looks as simple as a hotel wall console or can be fully ducted like a conventional furnace.
DX or water source can both be employed for this.
J