A little more info is needed. If you want this to operate outside of your own locally hosted network, it can get a bit more involved than you may be thinking about.
If this is going to be used by customers, and/or have any purchasing or ecommerce; I would recommend using an established mid-size or larger company to make an app. The app may be simple; however, security and hosting services can ramp things up quickly.
The reason is support. Think about how many times an app on your phone gets updated for 'bug fixes'. That means at least someone is having issues because of software. You don't want to field software questions from customers.
If you just need something that is only operated by one or two people, and it falls into an 'IoT' category where something commercially available may already exists? There are companies that have an 'App Builder' or make small scale custom apps on the IoT backbones of established services.
By using an established IoT service, you are more likely stay updated.
A lot of this stuff has become a lot more specialized which can be good and bad. If you are looking for something in a specific industry there is probably a provider that has something off the shelf, it could be industrial or machine control, ecommerce and ordering, sales, oil & gas, ag, etc..
