I've personally built three stilt houses. When I say built I mean I designed and got plans sealed by engineer. Pulled permits and dealt with zoning for variances. Then swung the hammer and hired plumbers, electricians and A.C. guy. But I pretty much did everything else.
If in flood zone your flood insurance will be about 300.00 a year and your homeowners insurance will be a lot less than those houses sitting on ground. I pay about 1200.00 a year.
Looking at house it's been there a while and from it's location has survived some pretty bad hurricanes. That's a plus on construction without looking at it.
I live in a stilt house right now. It cost me 125k to build and that includes land. BTW that was 25 years ago too. We just sold one of the others exact same floor plan. Same exact house for 325k, the other was 160k sold it for 280k
As far as insulation goes. There is insulation in ceiling. That's a finished ceiling in pic not the roof decking. Plus you must meet codes on residential homes and it must meet SEER guidelines for A.C. as far as insulation \Windows ect.....just meet building codes. Gotta be insulated some how. BTW half My house does not have an attic either, has a vaulted ceiling. But there's still insulation between ceiling and roof decking. R21 if I remember right.
My house is 25 years old. If your handy with paint and hammer you'll have no problems. If stairs are solid don't worry about them. Besides they look pretty cool.
The things I'd do if buying is a termite inspection. Plus look at roof or any signs of leakage. The deck is a give me here in Florida. I just replaced my deck and outside stairs that was exposed to the sun. The deck under cover looked new still. Oh yeah look closely at pilings also. I did concrete pilings.
I like the house though. A one plus one might hurt resell value in future though. But if it suited my needs I'd go for it as along as it's structurally sound.
Here's view out my sliders. Living elevated has it's advantages. Harder to climb in Windows lol and no peeping Tom's looking in either. I'd make an offer on it though. I'm sure they want to sell it. Plus with a 1+1 don't have to worry about people wanting to move in with you. LOL