Looking for supplier for thermal flat panels + system sizing help

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Taos, NM
Hello all! I have an existing two 4x8ft panel passive thermal array on my roof which has provided me with plenty of free hot water in the two years I've owned my house. It uses a glycol loop with a heat exchanger and passive circulation in an old, non working hot water heater I'm using as a storage tank.

I have a radiant heating system in my floors, in the slab I'd like to build a thermal array to heat. Since I have no other heating source, I know I'll need a lot of BTUs, and I roughly calculated that I'd need about 8x the 4x8 panels to get enough sunny-day midwinter BTUs to warm the house on clear days. I do have a wood stove I use for storm and backup heating, so this system is to cut down on the wood use and keep the floors comfortable in the day.

Previously, I had a 90k BTU hybrid propane hot water heater warming the floors via a flat plate heat exchanger, but I think due to the efficiency loss in the exchanger it just couldn't efficiently warm the floors. The sizing I came up with for the number of panels was based on estimating a 60% efficiency of this propane unit to put BTUs into my floors, which is a guess (I'm at 7k ft altitude so the propane heater was firing poorly and could not be compensated to run at my altitude so it is now a storage tank). The floors are 50/50 glycol because of my climate. I've been away all winter, and set up space heaters to prevent freezing, but the house seems to stay above freezing anyway without any form of heat aside from the large south facing windows.

Couple questions:
1. Does 8 ~35sqft panels (256 sq ft total) sound right, ballpark, for a 1400 sq ft house in a cold climate zone?
2. I've been working on the assumption that this is too big of an array to use a passive DC solar pump as my rooftop hot water heating system uses- any recommendations or are the standard taco pumps fine for this?
3. I've been putting a piece of plywood over one of my two collectors for the hot water loop during summer- what are you all using for a heat dump when the panels get too hot and you don't need the BTUs?
4. Finally, is there anyone that sells flat plate collectors to consumers willing to pick them up to save on shipping? It seems like SunEarth and many of the others don't sell direct. I'm planning to build this system myself, so that I can ensure it is done right, or redo it myself until it is done right.

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