The foundation of a great therapy dog starts with the right temperament, and that starts with finding the right breeder. Don't be in a rush, and don't have a certain timeline in mind. Look for a breeder that has produced other therapy dogs, and not just one...several. Make sure you're clear that that is your goal for your puppy, so you can be matched with a pup with the right temperament for the work. While Dobermans can make good therapy dogs, I think it's not necessarily the "norm" for them...the breed standard says they can be "aloof with strangers" and that's not uncommon, so it can take some extra work to find a Doberman who WANTS and LOVES to interact with lots of strangers and really, truly enjoys it. Not all of them do. It doesn't mean they aren't GOOD with strangers, it just means it isn't something they love and enjoy, so you do have to seek out the right dog for it. Again, there are MANY successful Doberman therapy dogs, so everyone doesn't need to jump all over me for this, but it's not necessarily our breed's natural inclination
Your puppy's early experiences with their breeder are critical to later success, so you want a breeder who provides great socialization - your puppy MUST have good, positive experiences. Take your time to do your research!
Think about what kind of therapy work you want to do...do you want to work with kids? Older adults in hospitals or nursing homes? The more variety of experiences your puppy has even before they come home with you (that are POSITIVE) will make a huge difference - not only with a large variety of people, but with different surfaces to walk on, with different equipment and noises...these early types of things can really set the stage for later in life. Then you continue this...a good puppy class that utilizes stuff like walking on unstable surfaces, exposure to different types of people and strange sights, all kinds of things as a first start, all in addition to starting your obedience foundation is what I would be going for. All this in addition to a pup that's outgoing, relatively calm, bombproof-type of personality....
Best of luck in your puppy search.