1) We do this because Jesus Christ is truly substantially present in the tabernacle. We are not kneeling to statues, nor to any priests or deacons near the altar, but to Jesus Christ in the tabernacle. We make the sign of the cross because this is an ancient prayer that identifies us publicly as Christians. Standing, I always make the sign of the cross immediately before I receive the Eucharist. I like to make sure I myself am in the proper frame of mind to consume our Lord. I also make the sign of the cross as a way of showing Satan - if he's watching, that it is Jesus Christ alone who I adore.
Remember that on Good Friday, we do not kneel when we enter church, for Jesus Christ is not in the tabernacle. The tabernacle doors will be open, and He will not be there. For me this is a terrifying experience, and I can barely hold back my tears when I see the tabernacle empty. Jesus Christ did not have to come to save us, but He came. I'm delighted that He came, and it terrifies me to think about what this world would be like had Jesus Never come, if there was no tabernacle ever in which Christ waits for us... a hideous thing to imagine indeed!
2) I was never Pentecostal. I was born into a Catholic family, stayed Catholic, then left the Church to wander naively, then came home about twenty tears ago. I like to sing, and I go to church by myself to sing before the Blessed Sacrament. I stand, kneel, then sit in the front pew, directly before the tabernacle. If the doors are closed, Jesus Christ is in there. I start with an act of contrition, then I sing the Gloria and many other hymns of praise.
I sing How Great Thou Art, Be Not Afraid/Pescador de Hombres, Faith of Our Fathers, Amazing Grace, Holy Holy Holy, All Creatures Of Our God and King, Softly and Tenderly and many others, maybe for 30 minutes, maybe for two hours. In "How Great Thou Art", I change "Awesome Wonder" to "Adoration", since I am in adoration at the time.
I have a great voice for singing solo - not just the only one singing, but the only one within earshot!
I trust my guardian angel to sing the right harmony to make even my voice pleasing to God.
If others are present, I let them pray in silence.
You should try what I do, sing before the Living Son Of God in church alone. You may sing well or poorly, so long as you mean what you sing. You may also moan, shout, or speak in tongues, even though I do not. I do, however, hum or whistle hymns sometimes.
I think it is good to sing to please the Lord. It also is good to sing, especially The Gloria, to make it clear to Satan that you reject Satan utterly and adore God utterly. It can be dangerous intentionally to offend Satan, but I think we should do so as often as we think of it. Satan might try to get back at you later, but he wasn't going to be your friend anyway!
3) It's not actually called a sermon, but a homily. It is different from parish to parish, and priest to priest. The priest, or the deacon if authorized by the priest or bishop, should explain the scripture readings, and explain how they apply to the life of Christians today. That's why it's a little different at each parish around the world. Not everyone needs the same explanation.
4) You may choose a particular saint, and you should give big thoughts to this matter. EWTN.com has a great section about saints. I love them all, since they have done what I hope to do, receive eternal life in the joyous presence of God. I especially love Jesus Christ's Earthly "Dad", Joseph. Joseph's courage was amazing, exceeded only by his humility and love for his family and Creator.
I think you should study Saint Anselm. He was not really a scientist, but was a brilliant thinker. His skills in Logic match or exceed those of any other mere man or mere woman ever, in my opinion. Anselm's ontological argument for the existence of God is dazzlingly beautiful. You may read all about it in Anselm's Proslogium, translated best into English by Sidney Norton Deane about 100 years ago. Anselm lived about 900 years ago.
Welcome Home!
May your studies of all sorts, in Science and in your faith, be fruitful and genuine.
I am Roman Catholic.
Peace be with you.
EDIT: Burt Ghezzi wrote a great and inexpensive book entitled "The Sign of The Cross."
He explains much about this ancient sign and prayer.
If you can not afford to purchase the book,
please provide me the name of your parish priest or parish and location.
I'll make sure the parish comes to own a copy available for lending.
Peace be with you.