It's easier to be more detailed when you don't smush a dozen questions into the first post
If you want to go more in depth with a specific question then say which one, but for now I'll just try to expand on what I said...
Do we think that we are the only True Church?
The Church is one ("one, holy, catholic, and apostolic"). It is the one bride of Christ, not a polygamous marriage (Eph. 5). The body of Christ was meant to stay unified, not fracture into competing but equal portions.
"There is one body, and one Spirit, even as ye are called in one hope of your calling; One Lord, one faith, one baptism, One God and Father of all, who is above all, and through all, and in you all." - Eph. 4:4-6
"But now are they many members, yet but one body. And the eye cannot say unto the hand, I have no need of thee: nor again the head to the feet, I have no need of you. Nay, much more those members of the body, which seem to be more feeble, are necessary: And those members of the body, which we think to be less honourable, upon these we bestow more abundant honour; and our uncomely parts have more abundant comeliness. For our comely parts have no need: but God hath tempered the body together, having given more abundant honour to that part which lacked. That there should be no schism in the body; but that the members should have the same care one for another. " - 1 Cor. 12:20-25
Can`t there be no other true Church?
There are grey areas, and fuzzy scenarios, but the foundation of it all is still no, the seamless garment can't be ripped. Now, whether, say, churches can be out of communion for over a millenium and both be part of the true church, I don't know.
Do we claim to be the only ones who have Christ , God and truth?
Individuals, and individual groups, have Christ, God and truth to varying degrees. No one is completely without light to see with. Some just have plenty of natural light, while on the far end in the opposite direction they have a flashlight that is running low on battery power.
Can we have the fulness of truth and can anyone have the fullness of truth, now really?
Orthodoxy = yes. Individual Orthodox = no.
If God is guiding and part of the Church, then the Church can have the fullness of truth. As soon as humans have a part to play there's a chance they'll mess it up. And humans don't really have the fullness of truth, even in dogmatic issues (because even if the dogma is true, that doesn't mean that someone fully and infallibly understands the dogma, it's implications, etc.)
Why doesn't this fulness of truth give us the ultimate truths to things even to biblical things?
We are limited by a number of things, though the root of it is that we are created and fallible.
We are created, therefore we aren't perfect. I guess I could include some bit here about how God won't make us understand because it would violate or free will or something.
Are we the only ones who have truth?
Various people at various times have various degrees of truth for various reasons. It's varied.
Others religions do not have truth?
Other religions have truth. So do other people. Otherwise how could God judge them fairly? Nay, how could God be judge to leave them without light in the first place? If others did not have truth, we would know God to be a tyrant and a fiend.
What about salvation?
Up to God.
God judges all. Being in the Church doesn't guarantee salvation, and being out of it doesn't mean you're screwed. Even if I were to be full-blow, uber-dooper-super Orthodox, I'd still view my Roman Catholic grandfather as having a better chance than me.
Can we not say that we are just one of those?
One of what?
One of what?
Isn`t the One True Church thing a human flaw, a thing of pride?
The Church is theanthropic. Insofar as it is divine, it is healing and perfect. Insofar as it is human, it is subject to harm and flaws. The more you follow the divine, the better off you are.
Humans are flawed and prideful, and can indeed make idols out of things, even good things. But making an idol out of an icon or hymn or sacred text doesn't mean that these things aren't useful. And the Church goes beyond this, because while icons and hymns and sacred texts are merely inspired by God, the body of Christ is, in some sense, actually God.
I want an answer to all this questions..
I gave answers. Whether they're correct or not is another matter. See above.
I gave expanded answers. Whether they're correct or not is another matter, for you to decide. Please see above.