If we start with John the Baptist, the first thing which pops into my mind is that he was in the wilderness, I assume by choice, also fulfilling prophecy. He needed to be away from the bothersome Pharisees to be able to teach and baptize. There must be something to being alone in the wilderness which purifies, steeling one's resolve. Selfish desires definitely get put on the back burner.
Absolutely. In every way, John's position is totally opposite to that of the Pharisees. His location, his mode of dress, his diet, his activities - they're all such a contrast to what we know of the religious world of the Jews. In the eyes of the Pharisee, his behaviour was aberrant, "For John has come neither eating nor drinking, and they say, He has a demon." (Matthew 11:18). The believer in the Lord Jesus, who finds their strength and joy in Him, will always be misunderstood and accused by the religious world. The empty religious professor can never understand why the real believer does without the props and enjoyments of earthly religion, why they aren't "eating or drinking", figuratively speaking.
John's food was of a different character altogether, "his nourishment was locusts and wild honey." (Matthew 3:4). Some say that the "locusts" referred to here weren't actually insects, but some sort of fruit. I don't know whether that's true or not, but a diet of locusts would suggest moral cleanness, they were a clean creature according to the Law. ("Yet these shall ye eat of every winged crawling thing that goeth upon all four: those which have legs above their feet with which to leap upon the earth." (Leviticus 11:21)). These creatures who could "leap upon the earth" might suggest an ability to rise above the earth and be free of its moral influence. Leviticus 11:29 would be a contrast, the crawling things which were unclean. The dietary law teaches us that we're formed by what we eat, spiritually, and shows us the characteristics that spiritual food gives us, and the character that unclean things give us. I think we can tell a good deal about John because of his choices, as you helpfully point out. Wild honey was the other part of his diet. Perhaps that would also suggest purity - honey is a food which doesn't spoil - and sweetness. The believer's pathway is through a wilderness scene, but we'd be sustained by wild honey, the sweetness of divine things.
A garment of camel's hair and a leathern girdle were John's clothes. Camel's hair would be a resilient material, maybe suggestive of the protective nature of a near walk with God. A leathern girdle would also be functional and practical, and John was girt about his loins with it. In Ephesians, we're exhorted to "Stand therefore, having girt about your loins with truth..." (Ephesians 6:14). Girt loins in scripture is often suggestive of readiness for service, preparedness.
Then we have his mission: "Then went out to him Jerusalem, and all Judaea, and all the country round the Jordan, and were baptised by him in the Jordan, confessing their sins." (Matthew 3:5-6). Persons were drawn out of the city, and the region, and the country, to John and his baptism. Here were Jews who felt their sin and the sin of Israel, wholly unlike the self-righteous Pharisees and the heretical and exclusive Sadducees. By entering into the waters of baptism, they accepted death to themselves, and their disassociation with Israel's wanton sinfulness. I suppose that these were Jews who were wholeheartedly looking for their Messiah.
But, the Pharisees and the Sadducees came to the baptism of John, nonetheless. I've heard it said that "the devil is a regular churchgoer", and I'd absolutely believe it. He'll try to insinuate himself at every opportunity, and be ready to spoil and distract where He can. Thanks be to God though for the great gift of the Holy Spirit! "*Ye* are of God, children, and have overcome them, because greater is he that is in you than he that is in the world." (1 John 4:4). There is nothing the devil can do that can break in on the Spirit's power. John sends away these Pharisees and Sadducees with a rebuke and a warning.
But, yes, there is something about the wilderness setting here which is very distinctive. Here, John shows the character of someone to whom the world morally is a wilderness, without charms or pleasures, and whose food is divine, and whose expectation is the coming One. There is nothing selfish about John. He is nothing in his own estimation, as we see from his preaching in Mark 1 and his response to the interrogation of the Levites in John 1. I've often been led to imagine his feelings when "two disciples heard him speaking, and followed Jesus". There would be no bitterness or sense of abandonment in John's heart when his disciples left him - his joy would be full that these two had heard the glad tidings - "Behold the Lamb of God." (John 1:36) - and were about to go with Jesus and see where He abode, and abide with Him.