questions:
we will stay in the Spirit world, where all spirits of death people all going to be gathered...
and in this period the progress of spirit is going on (so there are more chances to bad people to become good)
Not really. People will in all likelyhood retain their attitudes they develope in this life. So if a person has evil desires in this life, they will have evil desires in the spirit world. But we believe that after Christ died his Spirit went to the spirits in Prison and he establish a program to precah the gospel to the spirits there. Now remember Paradise is for those people who were baptized and lived righteously. Now think of how many people in the world have not heard of Christ or have had the chance to be baptized. All of those people's spirits will go to Prison. But becuas eof Christ they will have the chance to hear the gospel in the Spirit World. So all those people who didn't have the chance to hear the gospel in this life will have a chance in the next.
But this isn't really about second chances. it's really about personalities and logistics. It is/was impossible for the gospel to go to every person in the world. So for those people who dies without hearing the gospel this will be their first chance. Simply put if a person would have accepted the gospel in life, but just didn't have the chance, then they will probably accept in the Spirit world. But if a person was bad and would not have accepted the gospel in life then they probably wont accept it in the Spirit world.
This is why we do baptisms and temple work for the dead. baptism and other ordinances are physical things. Spirits can not do them. So we must be baptized on behalf of them. This is then counted as their baptism and they can enter into Paradise.
Q1- How long we are going to stay there (Spirit world)? till the second advent of Christ?
It depends. The Spirits in Paradise will be resurrected around the time of the second coming of Christ. The Spirits in Prison will remain there until the resurrection at the end of the millenium just before the Final Judgement.
Q2- who were living before Christ, did they get immortal body, or still waiting his second coming?
the scriptures say that when Christ was resurrected many graves were opened up and people were resurrected. So we believe many of the ancient righteous people were resurrected after Christ was resurrected.
Q3- is this means possibly a criminal developes his spirit and may go to Terrestial kingdom for instance?
I would say that if a person retains their criminal mentality and they have not changed then they will go to the lowest kingdom(Telestial). But it's not up to me to decide that. Christ is our judge.
Q4- when God will provide them immortal body again?
Wicked people will get an immortal body at the end of the millenium.
Q5- is it going to be there same bodies as the one which they had on the earth?
People will have a perfect body. They will most likely look they way they do now except it will be a perfected version. So a person with a big scar on their face will not hav ethat scar. A person missing a leg or arm will have that arm or leg restored.
Q6- having immortal bodies include all the three states or just the Celestial kingdom alone?
All three. Resurrection and recieving a perfect immortal body is a free gift that Christ gave to everyone who chose to follow God's plan in the Pre-mortal life.
Q7- who goes to telestial kingdom, will stay there forever without any progress? or even a chance to go one step upper?
There are some people who believe people will be able to progress from kingdom to kingdom. But usually this is based on a few writings of Joseph Smith. But For the most part it is agreed that there will not be any progression between kingdoms. People will live with God's judgements for eternity.
Q8- who goes to Celestial Kingdom and become like God, what will be his/her purpose of eternal life? can he creates his own plan, or that still God's property?
This is an area of fewer details. All we really know is that we will become like God. God will always be our God no matter what level we reach. Just like my father is still my father even though I am a father also.
But my personal beliefs are that We will be allowed our own universe just like God in in control of this universe. We will be able to raise our own Spirit children and work to bring to pass their immortality and eternal life just like God did for us. Acoording to the Super String theory of science multiple universes and exist next to each other in virtually the same space. Kind of like a sliced loaf of bread. We would build our own planets and stars just like God did in our current universe.
Now about creating our own plan I really think that there isn't any other possible plan. The Plan of Salvation is only plan that works. So that same type of plan will be used in our own universes.
Now just remember this is my own personal rambling here. It's what we call "Deep Doctrine." When there isn't much official information but there is a lot of speculation.
So it's very similar to how life happens here. A baby is born. The baby grows and develops. Eventually the baby reaches adulthood. The now adult goes on to reproduce. Then a new baby is born and the cycle starts all over again. To me it is the same with us, "the god species."