On the subject of flashbacks, the bulk of advice I’ve received from agents, editors, and successful writers is, don’t use them unless there is no other way. Use them sparingly, and never use them near the beginning of a story. If a story cannot draw us in on its own strength, it will have no better chance later than sooner. If a story is strong, the reader will often resent being jerked from it into a flashback, and if the flashback is stronger, the reader will often resent being jerked from that back to the story. Jerky reading is seldom fun, and rarely gets past a first reader’s desk.
Yes, there are successful novels out there that are written in a series of flashbacks, but they hinge upon a story line so strong it is never lost in the flashbacks that blend to strengthen it even more.