I want to build this to circulate hat/warm water through hose coiled in pots to keep a small number of plants extra happy through our mild winter (high 30's - 60s during winter) If I build it this way, it will be closed loop and does not matter if the water is contaminated I guess...still, needs to be cleaned somehow.

i see no one said how to clean the coil, just the condenser. Is your furnace a up flow or down flow? Is the coil on top of the furnace,or under the furnace? If you try to use coil cleaner on you indoor coil you need to have a pan under the coil to catch all the water and coil cleaner. You do not want the coil cleaner to get on your duct work or on your heat exchanger. also be aware that a lot of these coil cleaners have a acid in them that you don't want to get on your skin or in your eyes. If your outside condenser coil has a lot of white fuzz in it, you do not want to put a water hose on it from the out side, that will only push the dirt in deeper into the coil. You need to to take the top off the unit and hose it from the inside out to push the fuzz out. later paulbm

Nowadays, equipment is very similar. Nordyne is good equipment (although all brands have higher and lower lines) with a good warranty. What you should focus on is finding the best contractor to install the equipment.

The ceiling above the crawlspace is the bottom of the first floor. The warm moist air in the crawl space will rise up into to house if there is no vapor barrier to stop it. I would expect a three year old house to have tight windows and doors. The crawl space might be a source of the excess moisture in the house. What size is the AC? I would think a 2.5 ton single stage, or 3 ton 2-stage AC would be sufficient for a newly constructed 1749 sq. foot single story house. Did the builder provide a load calculation? A 6-10 minute run time might be considered short cycling. How often does this happen in an hour and what is the outside temperature?