My Legacy came with HIDs so I never bothered to do anything with them. For the inside little lights, I just switched to LEDs with no issues. If you don't have the HIDs and have halogens, I'd recommend Morimoto2stroke 3.0 headlight replacements. I got those for my daughter's Impreza. Solved the issue of cheap LEDs not putting heat out to melt ice/snow.
I can't remember where I got firmware and nav updates from but it was free and self done. I got rid of my Legacy in '18 at under 80k miles so I haven't really kept up.