Hey Hellraizer. Those H&M units look really great. You seem to have a good grasp on things. Just a couple points I thought off.
You are going to need to be carful how you bring the chiller lines into your room. 50 degree water will be below dew point and will create a ton of condensation on them. My chiller has dual reservoirs and pumps. One reservoir is kept at 45 degrees for my air handlers which are fed from lines that run along the outside of the building and then through the walls directly into the back of the air handlers. The other reservoir is kept at 60 degrees and that runs through the manifold line that feeds the water cooled equipment (dehumidifier, Co2, nute reservoirs, etc..) that is in the grow room. With air handlers or large heat exchangers you really need to keep the reservoir for that unit 10-15 degrees below ambient temperatures to cool your room and help the heat exchanger run more efficient. If you are running a smaller load like nuglets then that obviously can be warmer. Since nuglets is cooling EVERYTHING in his room that creates heat with water he only needs that Ice Boc heat exchanger to cool the ambient room air. Snce he has an 8x8x7 tent he's only trying to cool 448 square feet which only requires 2,500btu of cooling capacity. Maybe a little more because of the climate where he lives. I don't know your exact situation but if you are trying to cool a larger area or have a 2+ ton heat exchanger then I would recommend getting either 2 reservoirs for your chiller or looking into another method to cool your nutrient reservoir.
You need to size your chiller accrding to your cooling needs. So if you need 3 tons of cooling for your air handler and you just want to cool your nutrient reservoirs also you are going to need a 3 ton chiller. Most commercial chillers over 2hp have internal reservoirs and pumps. If you are chilling less than that with say a 2hp chiller like nuglets then you will have a seperate reservoir like you stated. I just wanted to mention that cause I wasn't sure how big of a heat exchanger you were getting and I saw some of those H&M ones were 3 and 4 tons. If you under size the chiller in comparison to the heat exchanger then it's really not going to run efficiently. Your chiller will constantly run and if the sizing is not right then it may not even be able to keep the reservoir cold enough for the heat exchanger to do it's job.
If your chiller does not have an internal pump and reservoir I highly recommend that you get a good cast iron pump. They have multiple ports so that you don't need to run 1 pump for your chiller, another for your heat exchanger, and a third pump for your nutrient reservoir. Also, water flow with these heat exchangers is a critical element. Most pumps cannot handle the load required by heat exchangers; especilly when required to lift (push) the water 5-10' up to the heat exchanger. If the pressure is not there then the heat exchanger will not work properly. For your application look into a 1/2hp unit ($100). Flotec is really good and that's what I have always used but I know Durman and a few other companies make great units as well.
Hope this helps. Let me know if you need anything else.