Congrats and welcome to the forum! You can check for mirror caps through here: https://www.minimania.com/MINI_Cooper_Mirror_Caps_and_Covers
If you can't find any yellow caps, then just have it painted.
Try FITCAMX, they've been working great for me so far.
https://fitcamx.com/collections/mini
For the flaps, try checking out Amazon for a wide selection, or swing by your local car parts store. They likely carry Mini-specific options too.
My unc has a Chevy Bolt and wishes he'd gotten a Mini SE. It really comes down to personal preference though imo. But if I had to choose one, I'm choosing Mini.
Since Octopus communicates with your Mini directly, not through the charger, you'll want to make sure both your Mini and the charger are set to allow charging anytime. This will give Octopus full control over your Mini's charging schedule.
When you engage with the car, the center ring changes actively. It changes color in response to your actions, while the rest of the light strips in the interior remain solid. The solid color can be controlled using the upper panel's second toggle switch from the right.