So you have, at least for Munich and SE Germany:
Day one, Munich airport to downtown,
Day two, Munich downtown to Dachau and back,
Day three, Munich to Nürnberg and back,
Day four, Munich to Salzburg.
Day one, if you really know you are only going to your hotel in the inner zone and no farther, get a 4 zone Einzelfahrkarte (single trip ticket) for 11,60€. If there is any chance you might want to go out and explore after you get to your hotel, get a Gesamtnetz (entire network) Tageskarte (day ticket) for 13,-€. For 1,40€ more, it gives you unlimited use of the conveyances for the rest of the day.
Day two, for downtown to Dachau, use a Munich XXL ticket, for 8,90€, for unlimited use of conveyance in the inner two zones. A Munich XXL Tageskarte cost less than two single trip tickets (there and back).
Day three, a Bayern-Ticket, for 25€, single, will get you to the Munich Hbf by any conveyances, by train to Nürnberg and return, and give you use of any conveyances of the Nürnberg metro (VGN) while you are there. If you are within walking distance of the Hbf in Munich and won't use the VGN in Nürnberg, a Regio-Ticket München-Nürnberg will save you 3€.
Day four, again, a Bayern-Ticket (25€) is probably you best bet for a one-way ticket to Salzburg with use of transort to get to the Munich Hbf. If you only need the train from Munich Hbf to Salzburg, a Meridian Guten-Tag ticket for 2€ less will work.
Since you said "I", I assume you are traveling single. But if there are two of you, the same tickets are probably best, just a little more for two people.