I'm not sure i'd get the Phone mount. If you're doing it for navigation the Tesla native navigation is fine. I bought a screen protector for the Model 3 a few years ago but never installed it, screen glare doesn't really seem to be a issue.
But yeah about mud flaps I installed them after seeing how much got flicked up and it seems to make a nice job.
Probably the best investment was to get all-weather rubber car mats and boot liner. It's really easy to clean out, just take it out and wash it with a hose.
That and roof screens, in summer in Australia you can feel that heat.