May I ask if you can read German? There would be some primary sources, instructions written by Montgelas (as he wasn't there, he thought Metternich and the others to hold him in contempt for the alliance to France, rightly so) to the envoy to the Congress of Vienna, Wrede, who happened to be his nemesis. These instructions can be read in Quellen zur Geschichte des Deutschen Bundes, Abteilung I, Bd. 1: Die Entstehung des Deutschen Bundes 1813–1815. München 2000.

Montgelas was quite the extraordinary type for his time and place. In a sense, he was essentially a anti-Metternich by ideology and calling. He was a figure of the enlightenment, albeit an ultimately failed one. He even had to leave Bavaria for a while after it was found out that he was an Illuminati. Years later, after a strange life of politics, the constitution of 1818 gave Bavaria most of the things Montgelas dreamed of, but neither the King nor his successors nor the people proved to be too interested in the constitutional monarchy.

I read Eberhard Weis: Montgelas, Band 1:Zwischen Revolution und Reform : 1759 - 1799 years ago, but it was quite tedious, so I didn't read the second book, still it's the definitive biography of him.

In very short, the goals of Bavaria in the Congress were to retain their new territory and to stay independent.

Both things didn't really worked out the way the Bavarians wished, they had to give back Salzburg and Tyrol and they didn't like the compensation: Würzburg and retaining the Oberpfalz, also some small territories in the South. And they had to join the Deutsche Bund, which cemented their subordination to Austria.