(1) You may offer nafl salah before offering the fardh of Asr though the time of Asr starts already. It is forbidden to offer nafl salah after Asr salah.
(2) It is not right to offer all the salah before starting the journey. You should find out some way that you manage to offer each salah in its time. If you do not find time to get down from the bus then offer salah inside the bus. And if you find it hard to offer salah standing in the bus then offer sitting with indication, but in this case you will have to re-offer such salah.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband