My concern for you project is more the biological/composting side.
Your compost pile will have a lot of variability in the heating depending on what material you are able to compost. If you are able to get consistent material with consistent N:C ratio, then great! If you are using the material around you as is comes you will have a lot of variability in your system. In addition getting enough compostable material. Thus, I believe it will be compost limiting rather than pump/tubing limiting.
Before doing a lot of calculations, I would recommend getting some systematic experience first: getting a inexpensive water circulating pump (water recirculator (small) or someones broken hot tub pump (big), Craigslist maybe), cheap tubing and build a couple hot compost piles to get the feel for the composting cycle and variability in heat output during the compost cycling.