I think you cannot even have all the 25 or so applications currently available in FreedomBox running on a machine with 1 GB memory. Consider the list of apps in the Apps tab to be like an app store. You shouldn’t expect to have all available apps running at the same time on your FreedomBox.
Most apps in FreedomBox are quite light-weight in terms of memory usage. The most memory-hungry application is Matrix Synapse. You should avoid joining large chat rooms (more than a few hundred members) if running this application on a machine with 1 GB memory (this is also mentioned in the manual page for Matrix Synapse). The main FreedomBox server application (plinth) only consumes 60 to 80 MB of memory from my empirical observations.
You can run other external services on your FreedomBox if you want to. Just look up the minimum system requirements and see if you still have sufficient resources. For applications supported by FreedomBox, you can simply disable unnecessary or infrequently used applications to reclaim memory.
Regarding memory usage, I think we already have issues in the issue tracker for adding a swap space and showing minimum system requirements for apps. Another option called zram was discussed in the past but not implemented.