Yes, hell is eternal death. Heaven is eternal life. Hell is eternal death that never ends, total separation from God's love, that goes on and on. And yes, it is crowded. That is basic Christian theology.

You ask why could anyone else's prayers help you? If you are predestined, how could ANY prayers help you? I don't know, the whole idea of predestination makes no coherent sense to me.

We think of it like this: Christ is King. If you are going to the king to ask for things... You go to his throne to make a request... You see his mother there. Will it help your cause if you show great respect to his mother? Or give her a cold shoulder? Will that be taken as respect by Him or insult? If you ask her to ask Him also to grant your request, would that not help your cause?

Respect to the mother is respect to the Son.

All the saints and angels are alive and in the presence of God. They are there because they were holy enough. Some are more holy than others. Heaven is a hierarchy of holiness. Why not ask the holiest souls possible to pray for you? The ones closest to God. They can hear you if He allows it. Mary is the one who stands closest to Him. Just as she did at the foot of His Cross and when she bore Him in her womb.

By the way, we believe it is blasphemous to say that Jesus was born of an unclean vessel. He protected her from original sin in the moment of her conception. God would not make His human flesh grow out of a sinful body. He chose to create Himself out of a sinless Virgin, in every sense. A sinless virgin in the line of David. What kind of mother do you expect the King of Kings to have?