“Not all can accept this word, but only those to whom it is granted. Some are incapable of marriage because they were born so; some, because they were made so by others; some, because they have renounced marriage for the sake of the kingdom of God. Whoever can accept this ought to accept it.” (Matthew 19:11–12)
“He who marries does well; and he who refrains from marriage will do better.” (1 Corinthians 7:38)
I’m not sure what passages talk about the individual churches being individually governed, but every church has a certain degree of autonomy, and dioceses have fuller autonomy, though they of course have to accept official Church teachings.
“Calling no man father” is arguably not referring to the word itself:
“I do not write these things to make you ashamed, but to admonish you as my beloved children. For though you have countless guides in Christ, you do not have many fathers. For I became your father in Christ Jesus through the gospel. I urge you, then, be imitators of me.” (1 Corinthians 4:14-16)
“And Stephen said: ‘Brothers and fathers, hear me. The God of glory appeared to our father Abraham when he was in Mesopotamia, before he lived in Haran…’” (Acts 7:2)
There are also a few other New Testament passages that refer to Abraham as a spiritual father. So either Christians didn’t take Jesus seriously, or he meant something else: that we need to recognize God as our ultimate father and teacher, and not look up to people who adopt titles for themselves without putting into practice what they teach, or do not provide valuable guidance (Jesus also said to call no man rabbi/teacher earlier in the passage). Keep in mind that Jesus was a known user of hyperbole.
Baptism can be understood as superceding circumcision, which was performed when a baby was eight days old. It makes sense, therefore, to stick with that age. Additionally, a few passages make reference to people being baptized along with their “entire household.” Presumably, this would include children. After looking for them, I cannot find any Biblical passages that state that one must receive instruction of the gospel before baptism. (The Church does, however, require adults to go through the RCIA (Rite of Christian Initiation), which includes instruction on the gospel and Church teachings, before being baptised). I have not come across a passage that states that one must fully understand the gospel in order to be baptised, only that this is necessary in order to be saved, which is not the same thing according to Catholic teaching (and the Bible).
When you say that the original manuscripts called for full immersion, I assume you are referring to the fact that that is implicit in the Greek word for baptism. I fail to see that as being sufficient reason to require full immersion, as it is the spiritual aspect of baptism that is most important, with the physical symbolism being secondary.