Yeah. Assetforge pieces models together and let's you export them as a scene or complex object. I think you can use meshmixer and blender to make the exports more efficient for use. Assetforge is here: https://kenney.itch.io/assetforge. It's about 30 USD at the base price.
I see. Well, don't have the money, I'll handle myself on Unity xD, thanks again.
No problem. If someone makes a good tool in Unity to put together modular kits like this and supports multiple tiers, let me know!
heads up, learn a basic workflow to import content into blender, assemble and export to unity. It's free and it'll take you a day or so to learn, but it'll literally save you hours each time you need to work with new content.
All the scenes you see were assembled in Assetforge in a few hours. I put together 4 separate environments.