Most people don't have a static external IP address, so you will need to have an account on a dymanic DNS service. FreeDNS is the one recommended, but others are available.
If you want systems to be available within an ordinary web browser, such as Firefox, then you will need to obtain a domain name.
A list of other supported ARM boards can be found here, or you can install onto an old laptop or netbook. Some installation instructions for different use cases are:
* Typical installation * Installing on a Beaglebone Black * Installing on an existing Debian system * Installing on Armbian, for unsupported ARM boards such as Raspberry Pi * Creating a dedicated fediverse instance for a single user or to host a community * Deploying a mesh network which can operate with or without the internet * Adding or removing users * Improving security * Advice on setting up a mobile phone * Apps available on the system * Frequently Asked Questions