I am really interested in your project and I would be happy to collaborate with you. I have more than 5 years experience in Android app development and have all the required skills that you need.
During my career, I have implemented all the languages and technologies that you mentioned and came to certain conclusions. So, I am eager to share with you my knowledge and give you several offers.
Which refers to Java and Kotlin, I have experience in both of them, but nowadays Kotlin is more widely used. The first reason is that Android OS (operating system) belongs to Google and it announced that the Kotlin programming language is now its preferred language for Android app developers. Secondly, Google announced that many new Jetpack APIs and features will be offered first in Kotlin. So I would like to advise you to implement this programming language for your applications.