Need help and advise on designing a hot water system.

[J.P.M.]

McAdams ,"Heat Transmission", 3d ed., 1954 was the bible. I believe there are several ways to get it online in a PDF format.

It's probably been reprinted/updated by now, although, believe it or not, there isn't a whole lot that's new in heat transfer theory - more like new applications and more material adaptations.

Kreith is a better source for some of that, particularly solar thermal applications. Kreith: "Principles of Heat Transfer", 4th ed, 1986, ISBN #0-06-043774-X .

Do those for the basics before you attack the Duffie & Beckman solar thermal bible. You will do well.

[LucMan]

I got and read, Solar Engineering of Thermal Processes, I also ordered a copy of The Solar Heating Design Process by Kreider, and will read that as well.

The Drain back systems are looking pretty interesting, are there any issues from thermal shock, when filling the collectors, when the sun is on them and the collectors are hot?

Not a problem if you have the solar controller set properly. I usually set the pump to come on when the collectors are 15 degrees F above the the temp of the storage. Even if you would turn the pump on at 50 degrees above, the water doesn't just instantaneously fill the the collectors it takes several minutes to establish full flow.
On hot summer days the collectors easily can reach stagnation temps if you set the max water temp to 130 degrees F. The pump will turn of at 130 degrees and you would not be harvesting the sun for the rest of the after noon. That's why I set the max temp at 160 degrees F and install an antiscald or mixing valve on the outlet of the storage tank. Good quality flat plate collectors are pretty hard to damage unless there is a freeze up. That's why there are lots of AET and Sunearth collectors that are over 30 years old still in service.