Builder Recommendations and Insulation Advice for Buying a House in East Tokyo (Katsushika)

Hi everyone,
I'm planning to buy a house in East Tokyo, specifically in Katsushika, and have a few questions for those who have experience purchasing or building homes in the area.

I've found a local developer called Says that offers homes meeting ZEH standards (with solar panels installed), but their prices are about 30% higher than other new homes of similar size in the area. For example, a standard 3LDK (land area: 55 sqm, building area: 90-100 sqm) from a typical builder costs around 45-50 million yen, whereas Says is offering similar properties for 62 million yen.

Here are my main questions:

1. Builder recommendations: Are there any builders you'd recommend that offer good insulation and energy efficiency at a more reasonable price? Have you heard about Says before?

2. Buying land and hiring a builder separately: Would this be a better option financially in the long run?

3. Insulation and energy efficiency: Is it worth paying 30% more for insulation and other features? How can I confirm the insulation performance of a property?

4. Resale value: When considering long-term plans and potential resale, would it be wiser to go for the cheaper option to minimize future loss in value? Since the land price seems to make up a significant portion of the cost for the cheaper option, I’m wondering if this plays into the equation.

5. Hazard maps: I've noticed East Tokyo is generally more affordable compared to the west and has better access to Tokyo Station. Do you think Katsushika is a good area to buy in? Any concerns about flood risks or other hazards?

Thanks in advance for your insights!