Setting up a local RL environment in 2026 and WHAT I wish I knew!!!

I spent three days last month getting a reinforcement learning environment to run locally before I could write a single line of training code. Three days. For the setup. I'm writing this because I found almost no practical guide that covers the annoying parts, the ones that actually eat your time. So here's everything I wish someone had told me before I started. 1. Your "simple" environment is probably not simple I started with what I thought was a minimal setup: a custom browser-based environme