Question Advice on converting an existing 3D unity project to add AR mode?

Hi I'm still pretty new to Unity and very new to AR development, so in order to make my learning curve more managable I have built a small 3D unity project for a mobile game over the last few months, to get all the functionality and basic gameplay working first. The game is first person simple physics collection and puzzle game, and I want to add a room scale AR mode (a bit like the AR version of Angry Birds).

This is in Unity 2020.3.3f1

I've also done a few small AR Foundation tutorials just to get a basic understanding on the concepts and to test out simpler things like plane detection, placing and animating an AR object, etc. I'm initially targeting Android devices for my testing, but want to use AR Foundation to be able to also support iOS later.

As mentioned I'd now like to add an AR mode to my previous small 3D game project, and I'd appreciate any advice on the following:

• A sense check that my approach of developing in 3D first to make testing easier, than moving the game into AR is workable? Do more experienced AR developers use that kind of workflow or do you develop straight away in AR?
• Any tooling or assets that I should look at to make the conversion and AR testing process easier? I've found the AR Simulation package which looks very useful, but anything else people would recommend?
• Is there a way to convert a whole 3D first person unity scene into AR quickly? I realise the gameplay is likely to break and would need rethinking for AR, but would like to get a quick sense of how the assets look in AR.
• Any other tips or things to look out for in trying to convert an existing project to add an AR mode.

Sorry for the pretty general nature of this question - as I'm still a beginner at AR I'm at the 'I don't know what I don't know' stage!