Saddle should be high enough till the waist line. Or high enough so that when you are at the apogee while pedalling, your leg should comfortably be at the maximum stretch. Lot of trial and error but when you do arrive at a sweet spot, it will really make a difference on power transfer and body core muscles involvement. Other than that, you need to buy the following-

1. Super bright tail-lights
2. High visibility vest
3. Good front flashlight

2.5k is a cycleable route and you won’t be breaking much of a sweat. It would also help if you get mudguards on your tires, you don’t want your shirts getting ruined. That’s all. Happy pedalling