How to get shortcut key to do a specific task when it's more than one step in non-native app

I want my long press C to compose a text message in Verizon Message+. I can set the key to open the app, but I can't figure out a way to have it open a blank text screen.

In addition, if I wanted it to go even further, let's say open a text window to my husband, how do I set it up to do that if I am not using the native texting app?

Any help greatly appreciated!

It all depends on what your app supports.

By non-native, do you mean that the app is not set as default texting app? If not then it's quite easy.

If set as Default app, you can have a shortcut to Compose Text Message and it should give you option to pick from contacts.
Similarly, you can choose Text Contact and it would automatically open text window of your designated contact.

If you haven't set the Texting app as your default, then it all depends on what the app offers. You will probably need to use shortcuts from the app or by using third party app to create activity shortcuts that your app offers.