Does Postgres preserve insertion order of records?
The answer for this simple case is Yes. Rows are inserted in the provided order in the VALUES expression. And if your id column is a serial type, values from the underlying sequence will be fetched in that order.

But this is an implementation detail and there are no guarantees. In particular, the order is not necessarily maintained in more complex queries with WHERE conditions or joins.

You might also get gaps or other rows mixed in if you have concurrent transactions writing to the same table at the same time. Unlikely, but possible.

There is no "natural" order in a database table. While the physical order of rows (which is reflected in the system column ctid) will correspond to their inserted order initially, that may change any time. UPDATE, DELETE, VACUUM and other commands can change the physical order of rows. But the generated values for id are stable and not in any way connected to that, of course.