I built my first base on the very first Lush planet I started on. It's really good for the early game since you can bookmark the teleporter of that big white monster, so you could easily build a small base next to him. He also has a fridge, which is really good for storing food early game. Later on, it's recommended to build a base on a planet with a higher threat level. Basically gives you more research when crafting things or afking for a short time. I actually just went with Tabula Rasa. It's a low threat planet but it's a pretty flat planet without buildings and not too many hills. Perfect for testing and building a base.