Heating the slab will warm the whole room. The best part is that the room will be warmer at the floor (where your feet are) than at the ceiling. I would not expect to get enough hot water from the geo system for this, but I could be wrong. The geo only makes hot water when it is heating or cooling air for the ductwork. There are geo systems that only make hot water, but this is a different animal. In the winter, I use all the hot water it can make for showers and domestic use.
I would not recommend installing the pond loop pipes yourself. Not because it is difficult, but because they use a specific type and size of pipe. The installer will probably go ahead and run the pipe all the way to the pond while he is there anyway. Installing the PEX tubing took me the best part of a day to put down 1800 sq ft in my basement floor.
By the way, I know this might be different around the country, but my system has 3000' of 1 1/2" pond loop. The rule of thumb for our climate is 500' per ton.
