The question(s) in general does not give account to the fact that it it in a completely different manner and meaning that Holy Spirit descends upon Jesus, than upon men; for is not it clear that Jesus did not at all need baptism, which is acknowledged by the baptizer John himself, who, in fact, says that it is rather Jesus who is to baptize him, John, than vice versa? (Matthew 3:14). Now, why it is more apt for Jesus to baptize John than vice versa? Because John's baptism in water is just a preparatory one before arriving of Him who who will baptize by Holy Spirit, that is to say, arriving of Jesus, whom, by those words that "I am to be rather baptized by You", John acknowledged as having already arrived.
Thus, this having been established, how reasonable is it to think that the Principle through whom the Holy Spirit is dispensed to humans, i.e. Jesus Christ, needs Himself to be filled with Holy Spirit as usual men need it? He who has Holy Spirit in Him measurelessly (John 3:34), does or can He need any more? Not, of course, for there is no "more" to infinite. And what it means that Holy Spirit is infinitely present in someone? Nothing else than this someone also, just like the Spirit (1 Cor. 2:10), has infinite knowledge of God whose cognition is infinite (Psalm 147:5) in immediacy, in actual infinity and not processual infinity, like humans, for humans and angels have Holy Spirit's presence in measured way and in a processual way of growth, whereas the Son, Jesus Christ, in immediacy of the actual infinity. That's why He divinely says a thing that in tongue of even the highest of the angels, to say nothing about prophets or apostles, would have been a blatant blasphemy: "As the Father knows Me, so do I know the Father" (John 10:15).
Thus, the bodily appearance of the Holy Spirit after Jesus' baptism did not have any cleansing or bettering significance for Jesus Himself, to be sure, as the coming of Holy Spirit has with reference to usual men, for the Holy Spirit is called also metaphorically "Fire" by John the Baptist (Matthew 3:11), and this "Fire" consumes sins in human fallen nature (cf. Hebrews 12:29) turning human into a "new creation" (2 Cor. 5:17). But, Jesus Christ, who has no sin, how can He be cleansed by the Holy Spirit, from what? And therefore the bodily, dove-like appearance of the Spirit had only a pedagogical significance, not ontological significance, for humans present there, and this divine pedagogy was that humans may not be scandalized with reference to Jesus, taking a good courage to follow Him for He was attested by both Father and the Holy Spirit to be the Father's beloved Son ("You are my beloved Son" /Luke 3:22/), to whom they could listen and follow without any qualms or suspicions.
Now, this was a crucial matter. As to the other questions, for a clear vision of those questions it should be firmly established that Holy Spirit's presence has many different gradations, for not only the apostles, but even prophets who are lesser than the apostles, enjoyed a portion of presence of Holy Spirit through whom they prophesied; and also the apostles enjoyed a presence of Holy Spirit before the Pentecost to a certain extent, for how else could Peter acknowledge the Lordship of Christ? Is not it only through Holy Spirit that it possible, as Paul clearly says (1 Cor. 12:3)? But the fuller and sin-defeating presence of the Holy Spirit, and such a presence as to embolden the apostles to preach to the entire world and overcome even the fear of death, came only after and through the Pentecostal descent of the Holy Spirit to their hearts.