Looking for an apartment/house

Munich has the tightest (and most expensive) rental market in Germany.
You will need patience, luck and a very good impression on landlords (who can literally choose between tens if not hundreds of applicants).
Even if you find something shortly after your arrival on Monday, it is likely that you can only move in two to three months later. So arrange for temporary accommodation until then!
“Affordable” is a relative term, but Munich rents do not generally fall into this category. Budget €1200-1800/month plus utilities (which might amount to another €150-300/month) to have a realistic chance!

Great to know! What would be the best website to use?

Quoka and Ebay Kleinanzeigen are the most established classified ads sites. Immoscout24 is good if you are willing to pay property agent fees.