The Hub is meant for multiple communities.
Use this instead as most of the work you describe is already done:
It will need updating to latest API’s and standards on both iOS and Android.
I have used this base successfully for several clients in the past.
However:
It is definitely not an easy or cheap project, though (including the expense of ongoing maintenance which will be annually significant) and you may be better off just relying on PWA’s now as both Android and iOS support real time notifications natively. I believe Google even support deployment of PWA’s onto their Playstore!
Good luck.