Postfix aliases db: No such file or directory

This is because you have

alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases

The hash: means, that you must have a database file containing the hashes, as described in Postfix lookup table types:

An indexed file type based on hashing. This is available only on systems with support for Berkeley DB databases. Public database files are created with the postmap(1) or postalias(1) command, and private databases are maintained by Postfix daemons. The database name as used in "hash:table" is the database file name without the ".db" suffix.

Therefore, as described in the documentation of alias_maps:

If you change the alias database, run postalias /etc/aliases (or wherever your system stores the mail alias file), or simply run newaliases to build the necessary DBM or DB file.

This will build the /etc/aliases.db file from information in /etc/aliases.

Naturally you must run either of these commands also during initial setup.