Yes, Bratislava is near Vienna. I suppose you would need to check what you want to photograph in Bratislava and Vienna before making that decision. I believe the Autumn Rail timetable is out by now. When I was travelling in Europe almost 30 years ago, I relied on the Thomas Cook Railway Timetable. Of course, this was the dark ages before the internet.
By the way, have you sorted out your currencies yet? Most places use Euro, but not all. Trying to find places to change your currencies can be a pain in the neck. You would need to check which are the weekends because banks don't open so you need to have the currency in hand before that. On my time, there were Belgium, French and Swiss Francs, East and West Deutchmarks, Italian Lira, etc. Life is much easier with the Euro these days.