Will be appraise with the most comparable sales, obviously the same floor plan, same age and same square footage is the perfect comparable. The only time appraisers will go out of your inmidiate community is if there is no recent sales in your inmidiate community. I hope this helps.
The fact is that no one can predict the real estate market. New construction is always a higher price per sq. ft. because it is brand new!! (just like buying a new car) In new construction, you can choose interior options instead of dealing with whatever a resale house has to offer you.
As for the appraisal process, you cannot guarantee the new construction will appraise. Just because they offer other floor plans, appraisers are human and their opinions sometimes vary. New construction has a much better chance of appraising for list price but as a Realtor who works directly with a builder, it's not guaranteed!!!
There is not one person that can tell you what the market will be like in 5 years... heck, at this point we can't even predict it for the next few months!!! You have to be sure when you buy a home you buy it for a good market value price FOR TODAY'S MARKET. That's all you can do!
Good luck!!! If you are not working with a Realtor to represent you, feel free to call or email me. Even when buying new construction, it's always good to have someone on your side.