Is Istikhara considered valid if the supplication is made only before sleep without prayer, with the designation of signs (silver or gold) to indicate a specific time, and does the vision of two beads missing from the prayer beads symbolize a certain period (like two months or two years) for the wedding date?

What you did was not a legitimate istikhara, but rather an attempt to know the unseen, which only Allah knows. You must turn away from these matters and strive in supplication, especially during times of answer, along with fearing Allah, which relieves worries, for He says: "And whoever fears Allah - He will make for him a way out And will provide for him from whence he does not expect." As for dreams, one should not become attached to them and build the future upon them, but rather rely on Allah and entrust the matter to Him.