If it were me, I'd make sure the foundation and various building systems (water, heating, electrical service) were what they should be from the beginning. You'll be hard pressed to change or improve them easily thereafter.

After that, I'd look to be sure plumbing, lighting fixtures (exterior and interior), controls and any other built-ins were what you wanted.

You can easily remove, add to or change interior finish materials and colors. It's all the built-in stuff that's costly to change later.

That said, there's an old saying in construction along the lines of "anything can be done, it's only time and money!"

Good luck on your project.

I would add, that the "we will do it later" for me has historically ended up in "never" or 10 years later. ;) We wanted to wait to see what called to us for a backsplash, lived without one for 10 years. Just finished the basement bathroom , a project we talked about 11 years ago, only did it because my realtor said we'd need to.

That said, my friend went with a laminate countertop with plans to upgrade later and ended up loving her countertop! So some finishes like that may be a good thing to go lower end on, if saving money. I know someone else who went with a very basic base molding and then added on to it with shoe and a top piece later.

virgilcarter has it right- make sure the basic structure has good 'bones'. Strong, energy-efficient construction and long-lasting exterior finishes. Spend your money on good windows, too.

You certainly can keep the interior finishes simple, and upgrade later, especially if you can do some of it yourselves. One warning- if you have stairs, adding hardwood floors later on can mess up the height of the first step, which is not code legal, and is a hazard. Whatever thickness you add to the floors, you would have to add to each stair riser as well.

crown moldings, countertops, cabinets,
sinks, toilets, faucets and lighting fixtures
come to mind about easy enough to upgrade later.

invest in above minimum code insulation package,
air sealing, duct sealing, properly sized, above
minimum efficiency hvac system.
keep in mind that in
May of 2013 gas furnaces north of mason dixon line
minimum efficiency upgrades from 80% (afue) to 90+% afue.
windows should be shopped by solar heat gain coefficient
(shgc) & ufactors. look for nfrc label on brands you
chose. both shgc & ufactors should be less than .30
if you plan on using recessed cans..
Insulation Contact Air Tight. buy by the case for a
minimal upcharge from IC lights. the ICAT cans are
air tight and stop air leakage & insulation particles
from entering the house. to retrofit one IC to ICAT
is approx the same cost as purchasing ICAT by the case.

invest in air sealing as the house is constructed.
sites like southface inst has excellent air sealing
pdf's that you can download.

remember that code is a good thing. keeps you safe.
but it is the minimum allowed by law. hvac systems,
insulation packages above code is a good investment.

plan for efficiency. cost is upfront but savings
is long term.

hire an energy rater for specific info for you
home. Resnet & BPI have trained experts to put
together an efficiency package for your home.

best of luck

Thanks for all the great suggestions, guys!

We are definitely planning to make structural integrity a priority -- we are hoping that this will be the house we'll spend the rest of our lives in (and we're only in our 30s).

Anything that needs to be behind the walls like audio visual cables, central vac with hide a hose, security wiring. Put plenty of thought into how you will use your HVAC so that appropriate zoning can be included.