Thx for the response!

"Depends on how cold it gets there. Anytime you have water in freezing conditions, you're prone to damage from the water expanding/freezing."

RESPONSE: I live in MA, so there are freezing winters, but my thinking based on your answer is that so long as I blow out the pipes, I should be fine. I just wasn't sure if I had to bring the panels inside for the winter, but I guess not.

"It does not need to be perfectly diagonal, but the better the exposure is to the sunlight, the more heat (efficient) it will be."

RESPONSE: So, it sounds like that as long as the sun is hitting it, it's fine for it to stand perfectly vertical?

"Pumps are rated either Medium Head or High Head."

RESPONSE: Mine is a 1 HP Hayward Super Pump which at least one site says is a High Head.

"This corresponds to the amount of resistance to flow (feet of head or total dynamic head) the pump will experience. You should have a high head, especially when you place the solar panels on the roof.
Is it easy to figure out? Well, it all depends on pipe diameter, length of run, amount of fittings, rise of your roof, equipment used, etc... on the suction side and pressure side of your pump. These all have an equivalent pipe length that when added up will give you your feet of head.
THEN, you take that feet of head and compare with the flow charts of the pump you have to see if you will have enough flow to handle it."

RESPONSE: See this is where you lost me. And this is the part I'm nervous about. I know nothing about flow and valves and pressure... Right now the panels would be about 25-40 feet away, but once it goes on the roof it would be around 50 feet away (plus the height of a 2 story house). I guess I'd use 1.5" pipe? Do I need to worry about all this stuff?

"I believe the minimum recommendation is to have 75% of your surface area in solar panels. Yes, even a small panel will make a little difference, but it's your decision as to if it's worth it."

RESPONSE: If I could raise the temp 5-10 degrees with that number of panels, it's definitely worth it. I just wasn't sure if I'd only get 1 or 2 degrees.

"Installing these are simple enough. Run your pipe to the inlet header of your solar panels, after all your equipment (but before any chemical feeders), then run the pump from the outlet header of the solar panels back to the return line"

RESPONSE: This part I'm good on!