Does the dream I had after the Istikhara prayer indicate that the marriage to this young man will not be completed, even though I am still unaware of his characteristics and merits?

Istikhara is seeking the best (guidance) from Allah. It is recommended to add to it consultation with someone who knows the young man's situation. A dream after Istikhara can be a sign, but it is not definitive. Reliance in Istikhara is on the openness of one's heart and the facilitation of affairs. Istikhara can be repeated until one's heart feels at ease.