Matt, it seems there are a number of aspects to this: a) the design of the actual feeder; b) how to link and control multiple units; c) wireless access and control; d) mobile app;
a) when you say “I have designed” does this mean that you have a working prototype of a feeder, or is it at the stage of being an idea only? Can you share some details of how this is to operate, i.e. how the stepper motor and actuators are being controlled? Did you write the sketch for this?
b) will each feeder be a stand-alone unit, or will more than one feeding station run of a single microcontroller? Will each controller be accessed as a single discrete unit, or will there be a broker/server (e.g. a Pi) to serve as a hub for all the units? (The number of feeders that can be controlled per board will depend on the number of GPIO pins required to drive the servo, actuators and sensors on each feeder as well as wireless.)
c) how far apart are the sheds? Are they within the reach of a WiFi signal? Do they all have power?
d) will you be using an “off-the-shelf” existing app, something you intend to write yourself, or access something via a web browser or perhaps MQTT?
Perhaps the fist stage is to better understand what (a) looks like and your ideas for (b) as well as the answers to (c)? It might then be possible to start considering (d).