SpeedTwin newbie - USA

I recently moved to US. It's also my first experience with a heavier CC bike. I used to ride a 350 cc back in India. I got a 2021 SpeedTwin 1200 cc in California. I have a tall and thin posture.

1. I am looking at a good backrest for the passenger seat. Given the torque, I don't feel it safe enough for the pillion rider.
2. And how do people manage luggage when doing rides over multiple days riding solo? Do you just tie it at the pillion or get that luggage extension.
3. Also, any mods to make it better while cornering it on the twisties?
4. And did any of you replace the default headlamp?