You can run an entire, productive modern Linux, (minus a modern browser*) on 128MB of RAM and one slow core. If you push lower, you start running into issues. I would recommend having around 200MB or so of swap for sudden spikes of memory usage. An aggressive userspace OOM killer may make life easier. On Linux, if you just run SDDM that launches xfce, you will quickly OOM the system, because SDDM will stay in memory.…
Server side rendering will collect(steal) personal info, it is a no go. The only right solution is online services to provide a web site on the side of a whatng cartel web app, if the online service does fit ofc. No other way, and hardcore regulation is very probably required.