How hard can this be?

I think this is the correct thread section, so I'll post here.

I would like to make an "interactive chat story" android app. It's like a fake chat where you can choose pre-setted answers/questions and the story goes on in different directions.

The first thing I need to do is find a layout like WhatsApp and it needs to fit the user's phone (every phone screen). I don't know if the next steps will be harder or not; I have some experience in programming (c++, c#, I used unity for a period of time).

How hard can this be?

Should I use Unity or there is something better?

I think you can buy apks like these online then just mod and reskin it

I'd like to know where to find apk full projects as well.

I've downloaded more than 200 Unity Assets torrents, but 99% of them are focused on gaming.

Would be nice to have some edge on utility development as well.

You want basically a bot chat type app with whatsapp reskin:

https://codecanyon.net/item/facebook-messenger-chat-with-bot/15863870?s_rank=1
https://codecanyon.net/item/support-board-chat-and-help-desk/20752085?s_rank=23

I usually use codecanyon to buy scripts or chupa mobile

As i have developed some apps in the past i think this not will be very difficult, better knowledge you have better it will be.

If you have some experience with C# i would suggest going with Android studio and Java. Java is very very similar to C#.And since this is more app oriented you would use the native UI of android.This convo with predefined questions is implemented with something called tree . Read about it and yes its not very hard to implement.Also where you are going to store the questions - locally on the phone or on some server.