You learn what is evolving, and you grab onto it, and evolve right with it. This is easy territory for flame wars and "whatever fits you"/"there is no best stack", but that's not the full picture.
Your survival depends on what you know, life is full of surprises, death in family, cancers, car accidents, addiction, breakups, and depression.
Imagine a warrior, ask him, "what is the best weapon?" and can you really imagine him saying "There is no best weapon", no, s/he would never say that.
You go on the most popular code hosting website, you sort by number of stars and begin at the top.
To give you a specific answer "iOS, Android and a Web App" in context of "Inventory Management - Dealer Management - Accounting - Payroll - Analytics" is Apache Cordova, (iOS, Android, and others), you use npm/node this way you will have one code base, you won't have to write the same code in multiple languages (just imagine scaling a live data sync requirement in one app and then standard REST in another -- keep it all in one language, or you will fail.)
"Inventory Management - Dealer Management - Accounting - Payroll" is all pretty simple (but, please explore ideas like http://vorpal.js.org/ just to develop your API before getting to G-UI, finish your programs in the terminal first.
Don't pretend programs are written GUI first, they are not. GUI is a leaky abstraction to say the least.) Don't fall for redux, relax and use https://github.com/mobxjs/mobx for actual GUI, (by the time you get to this part https://vuejs.org/ will rule)
And for your Analytics front-end D3, it is a departure from standard JavaScript but it has a lot of love inside.
Finally, remember develop commands/API first, get your apps working in the CLI and you will finish your program before starting it. Think about using the power of Unix (https://www.npmjs.com/package/commander), for the love of all that is mighty think about IRC, NOBODY! has time to learn to use your apps/GUI and NOBODY! ever needed to learn how to use Siri, so create a Command Line Interface version of your program and before you jump to React/Vue meditate over https://hubot.github.com/ and programs like Siri.
Finally, if I was facing your requirements, I would build a wiki/forum where your users would interact with bots. Over time I'd rip put some of the robotic guts and boldly go where humanity needs to be headed, I'd replace them with what I call Artificial-Artificial Intelligence, networks of Human Mechanical Turks where anybody could participate.
Neural networks are easy to train, but they are also easy to trick. Nothing will beat a random sample of Humans from across the world reaching a consensus on a tough decision.
In closing, People, Real Hearts, Human Minds, powering your network would share in your profits, and you'd do your part in battling what ails us all, World's Poverty.
If a mother in Rwanda and a Boy in India participating in your Mechanical Turk can find their way out of poverty, by helping your to detect fraud in your circuit. Then, you did your part, to help Humanity grow.