Setup Raspberry pi(Zero or 3) components, boot up and connect to internet either with HDMI cable and keyboard & mouse Or headless( lot of tutorial available in youtube to setup headless).
Go to terminal for metasploit set up(if you are using through headless then you are by default in Terminal)
Update the Raspbian OS.
sudo apt-get update
sudo apt-get upgrade
Then just fullfill the dependancies.
sudo apt-get install build-essential libreadline-dev libssl-dev libpq5 libpq-dev libreadline5 libsqlite3-dev libpcap-dev subversion git-core autoconf postgresql pgadmin3 curl zlib1g-dev libxml2-dev libxslt1-dev libyaml-dev nmap
sudo curl https://raw.githubusercontent.com/rapid7/metasploit-omnibus/master/config/templates/metasploit-framework-wrappers/msfupdate.erb > msfinstall && chmod 755 msfinstall && ./msfinstall
./msfconsole
Or
msfconsole
It will ask you to set up new database, Type y or yes to continue.
BOOM ... Now you setted up Metasploit completely & you are in msf console..
To check the database status type the below command in msf console.
db_status
[*] postgresql connected to msf