There is nothing to indicate a crisis of confidence in Parmenion before Issus, or indeed after. He was a very good and experienced commander, and he would have known it, not least because Philip made no secret of his admiration of Parmenion's talents as a general. The army was on a roll, with confidence and expectations high, and Memnon, their only adversary of any note, was recently dead.So I hypothesize that Parmenion wanted to kill Alexander before Issus because he wasn't sure who was stronger, the Persians or the Macedonians. Also, Parmenion probably didn't like Alexander's risky tactics which might have endangered his sons Philotas and Nicanor.
There is also a literary device going on here. Not only is Parmenion's opposition to Alexander's plans being used to undermine his abilities (as previously mentioned), it is also a device used to explore the nature of Alexander's kingship. The kingship Alexander inherited from Philip was one of being 'the first among equals'. His generals were free to speak their mind to him, and Parmenion's advice is used to show that Alexander sought counsel from more experienced commanders, but was able to trump it with his daring leadership. It is interesting that after Parmenion's death, we don't seem to hear of this advice being given to Alexander, and it may be being used to be indicative of an increasingly autocratic style of kingship - certainly part of Plutarch's theme of Alexander's rise and fall on the wheel of Fortune.
Unlikely. Alexander's treatment of the Greek mercenaries who fought for the Persians at the Granicus (he sold them into slavery in the silver mines), is indicative of the bitterness and contempt in which the Macedonians held those who collaborated with the Persians. Parmenion was actually in advance of Alexander's position at Tarsus, guarding the Syrian Gates, a pass from the coast to the interior plains over which Darius was advancing. As such, he likely had knowledge of Darius's numbers and that may have concerned him, but he would also have had confidence in the superior training and discipline of the Macedonians over a large portion of Darius's army.Parmenion probably made a secret deal with Darius.
If he eliminated Alexander at Tarsus, Parmenion would have given himself two problems instead of one: Darius's army and convincing the Macedonian army to accept him as commander. Alexander of Lyncestis was still alive at this point and there would have been those who would have advanced his claims to the kingship, or Arridaheus. Parmenion was not of royal blood, so it is unlikely he would have been successful in making himself king, and he wouldn't have held the army together without the authority of a king, never mind what would have happened in Greece as soon as they found out Alexander was dead. Parmenion was too good a general to realise that giving in to Darius without a fight would cause more damage than it would achieve.
Very unlikely. There has obviously been lots written about this by every historian, but on the face of it, it would seem that at the least Philotas was guilty of laziness, stupidity, and opportunism in not reporting the plot. If he did know of the plot beforehand, then he clearly wasn't very well prepared. As I said before, Parmenion was in a position of power at this point, and if he decided to oppose Alexander, then Alexander had a major problem. Parmenion was executed, not because he was involved in the plot - and there is no indication that he was - but because it was normal practice to eliminate family members in a case of treason, assuming guilt by association and to prevent a blood feud from developing. Alexander had no option but to get rid of Parmenion as he would never be able to trust him again.Later Parmenio probably conspired against Alexander with his son Philotas: