To me this sounds like a standard block of flats essentially which will only available to anyone over the age of 55 ?
I would firstly recommend having stand alone smoke detection in each flat as you point out to avoid false alarm issues.
If built in accordance with current building regulations FLATS AND MAISONETTES don't need a fire alarm system covering the common areas.
However... that all depends as clearly you were intending to use the building as a sheltered scheme.
I therefore assume Building Control have dictated that a common fire alarm system be installed to probably L" standard?.
If that is the case then I'd also look at providing interlinked heat detection within each flat in addition to standalone smoke detection for added protection. Some of my colleagues here may feel that this is perhaps a little OTT. But I'd be thinking long term and how the health and mobility of residents may deteriorate.
With regard to the pull chord system my logic again is that as people get older, their health and mobility deteriorates. A monitored facility already in place to assist the resident in an emergency can only be a good thing in my opinion.
Secondly I would suggest that the common lounge could be converted into a charging room if required (complete with adequate F/R and detection of course).
I've never known of people of this age stealing electric from the communal supply, but if you were worried about that factor you could consider non standard electrical sockets or wired in spurs to stop illicit shannigans, have also known charging stations to be fitted with timers too.
With regard to using the room as a dumping ground, suck it and see, if it becomes a problem fit a lock, to which only residents with electric scooters have keys perhaps. I fthat doesn't stop it then you might consider warning residents that the room will be permanantly unavailable if unauthorised storage continues, and coupled with that try and establish why things are getting dumped in the first place - i.e do tennats need more storage space and if so can that be provided elsewhere somehow.