The U-Bahn, Trams, and Buses in Munich are run my the MVG. The S-bahn and regional trains are run by the Bahn. However, you don't have to buy separate tickets to use the S-Bahn/regional trains and the U-Bahn/trams/buses. The MVV (lit. Munich Transit and Fare Administration) coordinates the schedules and sets one fare system for the entire network.
There are a number of information centers in Munich. Most are run by the MVG and are in or near U-Bahn stations, but there are others, one of which is the S-Bahn Customer Service Center in the mezzanine above the Hbf S-Bahn station. I believe I have also seen an information center run my DB and MVV at the Munich airport.
Incidentally, if you wanted a ticket for the inner zone for a week, the 4 ring IsarCard for 21,20€ per person (42,40€ total) would be the best, but for 4 days, a Group Innenraum (Inner zone) Ticket for 3 days, at 28,20€ plus a one day Group Innenraum Ticket for 12,20€ (40,40€ total) would be slightly less. Also, depending on what you want to see in the Innenraum, a less expensive 2 or 3 ring IsarCar might suffice.
Depending on where you are staying and what you want to see, you might not even need transit passes. On our last trip to Munich, four nights, we stayed inside the Altstadt, a few blocks from the pedestrian street, and spent most of our time in the shops there and around Marienplatz (Frauenkirche, Glockenspiel, Hofbräuhaus, Maximilianstrasse). One day we used four single trip tickets (round trip for two), for 10,40€ (then) to go to the Deutsches Museum. That was our only transportation expense in Munich until the last day when we went to the airport.