Thanks a lot for your detailed guide!

So it all depends on whether the flight lands on time(which would be possible if there's no self transfers/check-in in between), and then I get my baggage immediately and finally finish my immigration process. I guess the entire process is gonna be a race against time in order to catch the bus which is expected to arrive by 10:40 at the Arrivals.

Carrying luggage (2+1 bags) with myself to the railway station and changing the station would also be a bit tedious.

I'll find out if there's any early arrivals to IAD or else, only option is to arrive late(maybe in evening or night) and stay over the night and leave early on the next day.