Also, as far as pump size is concerned, I don't know how small a pump you want to use, but I'm running this one:
0015-MSF2-IFC - Taco 0015-MSF2-IFC - 00R 3-Speed Cast Iron Circulator - Integral Flow Check, 1/20 HP
It's completely silent and runs at speed 1 (78W). I've got over 1000 ft of tubing with the longest loop being 250ft, and the pump has no problem achieving 1gpm flow, which is plenty for my purposes. The pump shouldn't need to run more than 15 minutes out of an hour, good insulation provided, which would put it roundabout 460Wh a day.