I've installed vinyl, fiber-cement, cedar, and T111 on SIP panels. Shouldn't be any problem, although nailing patterns might vary, depending on the material/manufacturer.

I think if you foam the attic, you solve all the problems with your last house. I built recently at the NC coast and we had 2 two ton heat pumps. It cost $1000 to upgrade both to seer 15. That also gave a better warranty. I think seer 15 is nearly always worth it in our climate. Now foaming the attic makes the payoff for seer 15 longer but still probably reasonable. Now if you told me you were building extremely tight and really minimize the East and West windows and shade the south ones, then seer 15 might not be worth it. That is why these questions are so hard to answer. Everything is ... it depends. But a decent generality is that if you have to have East and West windows in SC, seer 15 is worth it. One could build a house with a $100 a year a/c requirement in SC for seer 13 and then it wouldn't be worth upgrading to seer 15. I know you've decided to foam the roof deck but I always have to be the skeptic. My electric bills last year were $350 total for the 3 hot months. I am absolutely sure that foaming the attic would have saved some money. I am pretty sure it would be less than $50 a year. While we a/c longer than 3 months, those bills also include everything else electric. So almost 1/2 those bills are not a/c so I think they are a pretty good estimate of the total annual a/c use. Foam salesman will of course differ in their estimates. But the foam mostly only helps the upstairs system and my house (and probably your house) has 2/3 of the a/c use downstairs. Even if the foam saved 40% of my upstairs bill - it is about $50. Now foam also saves in winter but is often justified in a/c use. Comfort upstairs would be helped by rigid foam on the knee walls. This is a far greater ROI although honestly it still probably exceeds 10 years. I think you might be overkilling it to overcompensate for your last uncomfortable house.

The urethane foam roofing with which I am familiar requires a topcoat just as soon as the foam is firm enough to permit walking on it. Topcoats are acrylic or silicone. The topcoat protects the urethane foam from ultraviolet damage, which occurs rapidly and severely. Acrylic lasts 10 to 15 years and can/must be recoated as necessary. Silicone lasts a bit longer, but cannot be recoated. When the silicone ages out, all is removed and the whole process done over again.

I'll just add that I had my roof snow coated in September. "Snow coat" is the nickname of the white elastomeric coating the OP mentioned. The brand I bought at Lowe's does indeed have a ten year limited warranty. I think it ended up costing just under $400 for materials and labor. That was for a 14x56 SW. I hired an unemployed roofer from Craigslist who had coated his own roof and had two good references for MHs he had also snow coated. I plan to get a "roof over" in about a year, when I've saved up enough cash. However, there were two small leaks from last winter and I didn't want them to turn into big leaks, nor did I want new ones to appear. Also, unexpected things happen in life, and while I plan to have enough money saved in a year, I also have to plan for an unforeseen circumstance that could delay the roofover. It has now rained hard several times with no sign of any leaks, old or new. So even if something happens and I can't do the roofover for several years, I'm confident that the snow coat will do its job. That is worth $400 to me. I have no first hand knowledge of the "skin" type of roofing the OP was considering. What I have read matches up with what the OP was told. I'd be very curious to know if anyone here has firsthand knowledge of the rubber skin type of roof and what her or his opinion of it is.