Munich-Salzburg-Berchtesgaden-Hallstat-Vienna-Prague-Rothenburg OBT-Munich

For only 12 nights you are trying to see a lot but this is typical of many European itineraries where quantity is the goal. Since it is only 12 nights though, I say go for it! You will get a great overview of this part of Europe and you'll have just enough time to hit the highlights in each place.
The two days I am concerned about though, are your first two days when you plan to see Salzburg and Berchdesgaden. Coming from Singapore you are going to be extremely jet lagged. You have a full day ahead of you when you arrive early in the morning and you plan to see the city...know that you are going to be very tired. If it were me, I'd eat dinner around 4 or 5 in the afternoon of the first day and then go straight to bed to try to catch up on sleep to be ready for your second day of seeing Berchdesgaden and Salzburg. By day three you should feel better.

Hi Anita, Thank you for replying. I would do that, thanks for your advise.

I have a few questions though, is there any simcard dataplan that i could use to stay connected for all this countries?

For me it's just too much travel and too little time to stay in your destination. Only one full day for Vienna, one full day for Prague and other smaller towns even less, I would not like it.

Hmm. Not really, because i will be travelling first in the morning. For e.g Hallstat to Vienna abt 4hrs, if i travel at 6am, will reach vienna by 11, checkin and by 12 could do the tour, maybe walk the old town etc etc, but still i am open to suggestion, maybe i stay another day in rothenburg obt and get a train to munich on the 7th.

1. You are visiting 8 places (Salzburg, Berchtesgaden, Hallstatt, Vienna, Prague, Rothenburg, Schwangau, and Munich). You are doing that in basically 11 full days (the arrival and departure days are only partial and the arrival day will be jet lagged). Travel time will add up to more than three days. One day per venue is too rushed. Slow down!

2. The town is Rothenburg odT (ob der Tauber).

3. Was this posting really a request for advice or request for congratulations for being able to list all those venues in a short space?

By the way, "bus to Hbf, train to Salzburg"? The bus only goes to the Hbf, but most trains to Salzburg leave from München Ost (after the Hbf) and the S-Bahn goes directly there (also directly to the Hbf). Use the S-Bahn.

I agree with the folks who say you are packing in too many places in too few days. I have been to Europe many times, and I am always brain dead on arrival. When you get to Salzburg, you will probably be exhausted. So much for exploring Salzburg. One full day in Vienna is not enough, even if you arrive at 11 on the previous day. Trust me.

I would stay in Munich on arrival, and find a hotel that would let you check in early. I would also drop Prague.

With that said, this is your trip and your choice. But you did ask for feedback.

Thank you for the feedback, i have booked my trip and accomodatio , it is okay, i will only be visiting the main sights, i am also travelling first class via etihad so it wouldnt be that tiring.