@sirtom - Don’t know about your technical background. Can you please provide some basic information on your background - eg What programming languages do you know/have experience in, have you used a build system, major technologies that you have used. I’m assuming that you haven’t touched a build.gradle build file before, which is very surprising considering that the official Android tutorial gets into editing build files early on, which with Gradle requires knowing/understanding the traditional Gradle DSL (NOT the official Gradle Kotlin DSL) and the Groovy language.
Presumably you can use TornadoFX without a build system however you will find it very difficult to do it yourself (eg have to juggle dependency management yourself, manually manage the software development environment). Very much recommended to learn how to use Gradle as a build system, however if you want a much easier option there is Kobalt. Kobalt has a getting started guide (is a tutorial). The creator of Kobalt by the way is a well known former Googler named Cédric Beust (created the highly regarded TestNG testing framework for the JVM).