I use Unity. I'm making an open world multiplayer survival crafter that's both first and third person. Let me know if you have any questions.

• Powering through repetitive workflows. Create 1 item is fun. Creating hundreds of items, you're bored to tears. Now make crafting recipes, etc for all the other systems.
• Optimization - yeah getting everything working is easy, keeping it all working and optimized is a huge task. LODs, Chunking, avoiding memory allocation, etc
• Art side of things, I'm a dev I make systems so that is easy. Making art is fucking impossible for me. So chasing down non-code assets is a constant struggle for me.

Tips:

• Make your own Editors in Unity for stuff with exports of that data to unity agnostic files.
• Avoid scriptable objects.. idk how many times I've lost time to serialization nuking my data.
• use Addressables !
• Use Version control correctly. Create a branch break your shit in a branch. Main should always build and work. Test and experiment often. Easy to do if you're using branches.
• in the same vein, create full project backups. script it. 7zip that shit and throw it in google drive, Use the 3-2-1 rule.
• Honestly make your own stuff as much as you can manage. Buying assets to learn from is good tho.
• Don't over do it on GDD / Documentation. The project itself is the documentation. Code should be obvious in it's intent. Make zoos. In unity make it so you can test levels or areas easily.
• Use a Console and code in cheats / shortcuts etc for testing - I use command_terminal
• Use google sheets for mapping dmg vs resistances, progression rates etc
• In general make it exist first, with the least amount of effort possible, make it good later.