Can I access platform services and APIs like sensors and local storage?

Yes. Flutter gives developers out-of-the-box access to some
platform-specific services and APIs from the operating system.
However, we want to avoid the “lowest common denominator” problem
with most cross-platform APIs, so we don’t intend to build
cross-platform APIs for all native services and APIs.

A number of platform services and APIs have
ready-made packages available on pub.dev.
Using an existing package is easy.

Finally, we encourage developers to use Flutter’s
asynchronous message passing system to create your
own integrations with platform and third-party APIs.
Developers can expose as much or as little of the
platform APIs as they need, and build layers of
abstractions that are a best fit for their project.

Can I extend and customize the bundled widgets?

Absolutely. Flutter’s widget system was designed
to be easily customizable.