I have heard while listening to a documentary and lecture or two that the Roman emperor Marcus Aurelius was nearing a peace favorable to the Romans by the end of his reign but due to his passing and the succession of Commodus it would then not be achieved. Based on the sources at the time how true was this reality, at the very least of nearing an end to the wars after years of conflict?
Also a few further sub questions regarding the war:
How did the actual battles/fighting proceed? From what I’ve read Germania was a thick and dense forest at the time, so how did the Danubian legions fight the German tribes, was it a form of guerrilla warfare on the receiving end, a defensive formation on their side of the Roman border, formations similar to the late imperial period of smaller numbers, or where there actual pitched battles?
If peace were possible, with whom and how? From my understanding the tribes all maintained distinct identities and territories, rarely confederating as the Gauls did save for a few noted exceptions. Would all Germanic tribes in conflict with the Romans have agreed to this or would it be a certain few who took the most loss?
What would a Roman favored peace most likely look like that would have been satisfactory to the legions/Aurelius? Client state, tribute, territory etc?
These are excellent questions. Unfortunately (as I know from recently creating a podcast episode on the Marcomannic Wars), most cannot be answered with any degree of certainty.
Our two main sources on the Marcomannic Wars - the Historia Augusta and Cassius Dio's Roman History - are both problematic. The Historia Augusta, composed around the end of the fourth century by an anonymous author sometimes described as a "rogue grammarian," blends fact and fiction with willful abandon and obscure intent. Cassius Dio's 72nd book, which described the Marcomannic Wars, exists only in epitome.
On the wars' end, finally, we also have Herodian's History of the Roman Empire since the Death of Marcus Aurelius, which (if tediously rhetorical and often unreliable) is at least a fuller source. Here we told that Marcus was anxious in his final days about the fact that he had not yet pacified the tribes north of the Danube (1.3.5), and that Commodus was persuaded to abandon the war effort by sycophants in the imperial retinue, who longed to return to the pleasures of Rome (1.6.1-3).
By Herodian's account, the end of the war was in sight. He has Commodus' brother-in-law Pompeianus say:
"After you have conquered all these barbarians and extended the boundaries of the empire to the northern seas [this was almost certainly never an actual war goal], it will be glorious for you to return home to celebrate your triumph, leading as fettered captives barbarian kings and governors." (1.6.6)
Yet Commodus, Herodian assures us, failed to heed this advice, and ended the war by a judicious combination of delegation and bribery (1.6.8).
Cassius Dio (whose version we should follow here) agrees that Commodus withdrew from the war quickly, and that he could have completely destroyed the Marcomanni and other tribes of the Danube frontier. By his account, however, the peace that Commodus (or his advisers) imposed was carefully-considered, and made the Marcomanni and Quadi virtual clients of the Empire:
"In addition to the conditions that his father had imposed upon them he [Commodus] also demanded that they restore to him the deserters and the captives that they had taken in the meantime, and that they furnish annually a stipulated amount of grain...Moreover, he obtained some arms from them and soldiers as well, thirteen thousand from the Quadi and a smaller number from the Marcomani; and in return for these he relieved them of the requirement of an annual levy. However, he further commanded that they should not assemble often nor in many parts of the country, but only once each month and in one place, and in the presence of a Roman centurion; and, furthermore, that they should not make war upon the Iazyges, the Buri, or the Vandili." (73.2.2-4)
With another tribe, the Buri, we are told that Commodus granted peace on the following terms:
"...now that they were exhausted he made peace with them, receiving hostages and getting back many captives from the Buri themselves as well as fifteen thousand from the others, and he compelled the others to take an oath that they would never dwell in nor use for pasturage a five-mile strip of their territory next to Dacia" (73.3.1)
Commodus, in short, may have ended the war prematurely; but contemporaries probably did not regard his peace as disastrous or dangerous.
As for your other questions:
Besides the reliefs of the Column of Marcus Aurelius in Rome (which seem to have a tenuous connection with the realities of battle), we have only a few references in Cassius Dio on the actual conduct of the war. There were several large pitched battles. Cassius tells us, for example, that Marcus Vindex, the Praetorian Prefect, was killed on the field, and describes a battle between the Romans and the Iazyges on the frozen Danube, which is worth quoting at length:
"The Iazyges were conquered by the Romans on land at this time and later on the river. By this I do not mean that any naval battle took place, but that the Romans pursued them as they fled over the frozen Ister [Danube] and fought there as on dry land. The Iazyges, perceiving that they were being pursued, awaited their opponents' onset, expecting to overcome them easily, as the others were not accustomed to the ice. Accordingly, some of the barbarians dashed straight at them, while others rode round to attack their flanks, as their horses had been trained to run safely even over a surface of this kind. The Romans upon observing this were not alarmed, but formed in a compact body, facing all their foes at once, and most of them laid down their shields and rested one foot upon them, so that they might not slip so much; and thus they received the enemy's charge. Some seized the bridles, others the shields and spearshafts of their assailants, and drew the men toward them; and thus, becoming involved in close conflict, they knocked down both men and horses, since the barbarians by reason of their momentum could no longer keep from slipping. The Romans, to be sure, also slipped; but in case one of them fell on his back, he would drag his adversary down on top of him and then with his feet would hurl him backwards, as in a wrestling match, and so would get on top of him; and if one fell on his face, he would actually seize with his teeth his antagonist, who had fallen first. For the barbarians, being unused to a contest of this sort, and having lighter equipment, were unable to resist, so that but few escaped out of a large force." (72.7)
This, to the best of my knowledge, is the only extended description of tactics in the Marcomannic Wars that we possess.
Peace was negotiated through envoys sent by individual tribes (e.g. Dio, 72.15-16). Although the Quadi, Marcomanni, and Iazyges (to say nothing of the various other tribes involved) seem to have been loose confederations, they had enough coherence to conclude treaties (if not necessarily to keep them reliably).
At one point (if we can trust the Historia Augusta (24.5)), Marcus intended to create two new provinces (Marcomannia and Sarmatia) in the territories of the insurgent barbarians. Marcomannia, presumably, would have been located north of Pannonia, while Sarmatia would have occupied the salient between Pannonia and Dacia. Any tribes beyond the frontiers of these provinces would probably have been reduced to client status, responsible for sending some combination of tribute and troops.