Best practice for creating tablespaces in Postgresql
Tablespaces in PostgreSQL exist for some really particular needs (and I doubt a less than 500 GB is in that case) and for SQL compliance.
If you plan to create tablespaces to store eventually everything on the same disk, please don't. If you plan to create tablespaces inside $PGDATA, please don't.

Tablespaces lead to more complex recovery operations (if you need one). You'll curse yourself later, trust me.

You'll find a lot of excellent advices in Christophe Pettus slides (PostgreSQL when it's not your job). The slide 27 is about tablespaces and why not using them.