Best practice to move from MySQL to PostgreSQL

I've decided to change my application from MySQL to PostgreSQL and I'm
already sure, it's a good decision.

 From what I know, using PostgreSQL, all fieldnames should be written in
lowercase to avoid problems.

Unfortunately in MySQL my fields are named like this:

> BelegNummer, BelegDatum ....

so a query looks like this

> SELECT BelegNummer, BelegDatum FROM rechnungen ORDER BY BelegDatum ASC;

This will not work with PostgreSQL, because PostgreSQL will change all
fieldnames to lowercase, right?

Means, I've to change all fieldnames to lowercase like belegnummer,
belegdatum ....

Ok, that;s not a big problem. But is there something else I should do to
avoid other problems?

Should I change my queries to something like this:

> SELECT belegnummer, belegdatum FROM rechnungen ORDER BY belegdatum ASC;

or will Postgre do this automatically while executing the query?

I only would like to make sure, that I'm right until here and/or is
there is better way to convert an application from MyQSL to PostgreSQL
before I'll start to change everything.

Thanks in advance for your help.