Why couldn't the Holy Spirit come while Jesus was still among the apostles?
I'm not entirely sure, but I have a few educated guesses, for what it's worth. First, I think that as long as Jesus was on earth with the apostles, it was not really necessary for the Holy Spirit to be sent. Remember, Jesus' primary reason for sending the Spirit was to lead the Church into all truth. Once He is gone, they will need such a leader, desperately in fact. But, as long as Jesus is with them, this is not necessary.
Also, Jesus had to finish His work before the Holy Spirit could come and make it bear fruit in the Church. Once Jesus ascended into heaven and took His seat at the right hand of the Father, then the Spirit could get to work extending that reign in the world by moving in the sacraments and protecting the Church from error and helping men to pray and doing everything else that the Holy Spirit does. The Spirit's role in the Church is sort of dependent upon Jesus fulfilling His role first. I hope that makes sense.
Why is Peter never called “Pope” Peter? Always the “Apostle” Peter or “Saint” Peter?
I don't really know for sure. Perhaps it’s because, while Peter is certainly the first pope, he’s also much more than that. He is after all the only pope who can say he personally witnessed the life of Christ. Not only was Peter one of the 12 apostles, he was among the inner circle (with James and John) who received special instruction and witnessed certain events the others did not see. I think that, for this reason, in people's minds Peter is an apostle before he's anything else. Plus, the word "pope" emerged in the time of St. Leo the Great (440-461 AD) to refer to the successor of St. Peter. Peter, of course, is the original, so this may be another reason why the title never really caught on in reference to him.
Is it okay to swear on the Bible in court?
Yes. See the following paragraph from the Catechism:
2154 Following St. Paul (cf. 2 Cor 1:23; Gal 1:20), the tradition of the Church has understood Jesus' words as not excluding oaths made for grave and right reasons (for example, in court). "An oath, that is the invocation of the divine name as a witness to truth, cannot be taken unless in truth, in judgment, and in justice" (Code of Canon Law, can. 1199 § 1).
Is cloning okay as long as it is not human cloning?
From what I can tell, not very much has been said about this by the Church. The most authoritative statement I could find comes from the document “Reflections on Cloning” by the Pontifical Academy for Life. Part 4, para. 5 reads in part:
“There is a place for research, including cloning, in the vegetable and animal kingdoms, wherever it answers a need or provides a significant benefit for man or for other living beings, provided that the rules for protecting the animal itself and the obligation to respect the biodiversity of species are observed.”Human cloning is always forbidden.
After the Resurrection did Jesus stay on earth the whole time until Pentecost or did He come and go from Heaven?
He seems to have come and gone. In Lk 24 for example, we see that Jesus appeared on the road to Emmaus (vs. 15), then vanished from their sight (vs. 31), then appeared again (vs. 36). He did this for a period of 40 days (cf. Acts 1:3). Then He ascended into heaven and ten days later sent the Spirit on the Feast of Pentecost.