For me, the main question would be what's the main part of the story? What's the main conflict? You mention the character going on the road trip, and my guess is that's going to have to be the brunt of the story. The tragedies are what lead up to him going on this experience, right? So my main question would be what is it that happens on the road trip itself? What kind of conflicts does he face? Obviously, he can't just be going along and having fun and everything is going great as he sorts things out without any difficulty.
My personal, without knowing anything more, take on things would be to show the final tragedy leading up to him going (or the aftermath of it), and then having him go.
The biggest question, and probably the hardest to answer, is going to be how much of the tragic past is going to be important and necessary to know. Essentially, it's going to end up being backstory (unless you're doing a Slumdog Millionaire sort of thing where the story itself is the backstory and it's just told in the form of flashbacks). That means that when it comes down to it, most of that is probably not going to be incredibly necessary to know, or at the very least it might not be necessary to show in detailed flashbacks.
I mean, if the backstory just serves as an impetus for his going on the road trip, that could be summed up relatively easily in just a few lines. This is obviously not how you'd do it, but having a guy talk to his buddy and saying, "My dog died, my wife left me, my business burned down, my mom has Alzheimer's, and I just found out I've got Huntingtons. Yeah, you could say I'm a little depressed."
See? You wouldn't necessarily need flashbacks to any of that stuff at all because it's all backstory. It could be that there's a particularly tragic aspect of his past that's the hardest to overcome, and maybe that's something that you just sort of hint at for awhile and then reveal (via flashback, dialogue, whatever) later on as well.
This has been rambly and maybe hasn't made sense. The most important question, however, is going to be what is the story itself about in your mind. If it's about him going on the road trip and healing, chances are you won't need to bring in as much of his tragic past as you think. Just showing how those events have influenced his life, the kind of person he has become because of them, will give more characterization than just telling the story on it's own, IMO.
Hope this helps some.