I’ll be happy to help.
You can use https://dashboard.literatecomputing.com/ to create a new droplet and install Discourse there. You’ll select " Pro Installation (Custom SMTP) ($400)" to use your custom SMTP setup. That’ll get Discourse installed.
If you have an existing droplet named forum.example.com, please delete it before starting the installation. The script will create a new droplet with its SSH keys installed.
If you purchase that I’ll also help you get WordPress connected.