I recommend that you immediately do a search of the existing technology vendors who are already able to produce mobile-apps more or less automatically now.   (Much as there are well-established web site vendors who can produce mobile-friendly web sites, even at zero cost.)   Of course it depends upon the app, but if the purpose of the app is relatively similar to the present-day purpose of a web site, an app sometimes can be generated!   What I am saying is ... don’t jump to any conclusion about anything or any of your choices based on know-how that is even two years old.   Things are evolving that fast.

Nevertheless ... you need to begin this thing with a truly all-inclusive project plan.   You need to build the whole ball-of-wax scenario and then break that down into manageable steps.   Yes, Perl certainly can do everything that you want on the back-end.   Yes, the templating engine and so-on that you have mentioned are industrial-grade enough to get the job done.   All the plumbing parts you’ll need are there.   But that’s not the pressing design question you now face.

The things you “knew,” even about web sites?   Fuhgeddaboudit.   Do you think they’re going to just be accessing your web-site through a mobile vs. a standard browser?   Bah.   This is not just a new world ... it’s a new world.   Since you are embarking on a completely new venture, it is now profoundly important that you make the right decisions ... and your past experiences have virtually nothing to do with that.   I don’t think this can be emphasized enough.