Well you’ll need a SQL server setup. There are plenty of tutorials for that on google. In the Project Inventories config.conf enable MySQL and input the server database name, host, username and password. On your Minecraft server setup create your inventories with /inv create and assign them to the desired worlds with /inv set. Once this is done, on any other Minecraft server, in the config point it to the same database. Because the inventories have already been created all thats needed is to assign the previously created inventories to the desired worlds. Repeat with each server.
As far as Project Portals goes, You’ll need SpongyCord plugin installed and as previously stated when creating a portal, in the destination argument enter the bungee server name, and add the -b flag at the end.