While there definitely is a large difference in knowledge and experience between someone making their first bass and a bass maker who does it for a living, you both have to go through the same steps. If you want to learn how to make just one, you need to learn and execute the same steps that you would be using if you made one hundred. So you could become a maker with the intention of only ever making one for yourself, or you could do it with the intention of making more instruments. The only other alternative I see is "making" an instrument with an established maker who holds your hand through the process and potentially takes care of some of the tricky bits, but I doubt too many makers would want to do something like that when they could be working on their own, or teaching an apprentice/someone who wants to learn to practice the craft. There are plenty of talented repair people who don't make instruments, and plenty of them who have made one or two but are kept busy enough with other things in the shop that they don't/can't make an abundance of instruments. While there are a lot of similarities in repair/restoration work and making and a knowledge of one doesn't hurt the other, it does not sound like that is what you want to get into.
You might be able to find a luthier/maker who wouldn't mind a fly on the wall in the shop, but I'm not overly optimistic. Few people have room for an additional body in the shop when they are working, and few enjoy having someone looking over their shoulder. To give you an analogy to playing, few musicians would want to have someone sit in and watch them practicing, regardless to how much they enjoy performing. Even if that person isn't asking questions or getting in the way, you wouldn't likely feel comfortable with them intently watching you practice, and you would likely fell your work suffer as a result. The violin making schools might be your best option for something like that if they allow people to audit their classes but they might not allow it, they might only allow you to audit lectures/presentations instead of shop time, and there will likely be a fee involved.
If you are looking to become a maker, then your options are typically to apprentice, attend one of the schools, attend summer/workshop programs, or try to figure it out on your own. If you want to apprentice, you need to find someone who is willing to take you. Most makers want their apprentice to have at least a basic understanding of tool use, sharpening, and wood working, where others want someone with repair experience. Very few take "I've never held a plane before" people, unless they know them personally. Summer/workshop programs come in a lot of different flavours, but typically you are going to learn far more about tool use and the instrument if you start with repair instead of making. A violin maker gave me 350-ish hours as an estimate of how long it takes him to complete an instrument, so you can imagine how far you would get through the process as a first timer during a 40 hour course. The Chicago School of Violin Making is 3780 hours of class time, (which doesn't count the work you do on your own time) and they expect you to make 6 instruments, 3 violins, a viola, and 2 personal choice, in 3 years. North Bennet St. School is 7 instruments in 3 years, 5 of which are violins. While we live in an era when there is an overwhelming amount of information available to you online and elsewhere and there are some pretty good resources out there for instrument making, "So you want to make a Double Bass" comes to mind, there are a lot of questions along the lines of "does this feel strong/thin/flexible enough?" that are answered in person much better than by reading a book.
As far as the schools go, they focus on violins because they are smaller which requires less time and materials, because there are far more violinist out there than bassists, and because the skills/knowledge translates to the other instruments as well. Eric Rene Roy from Upton went to North Bennet St. and a few other bass makers got their start at violin making schools. If you are interested in Chicago specifically, it would be worth getting in touch with them and finding out were they stand on basses. There doesn't appear to be anything suggesting that the two "personal choice" instruments can't be basses, although they might advise against both of them being basses because of the amount of time you have at your disposal. The playing requirements vary from school to school as well where some of them say violin vs. violin family instrument, and the level at which they want you to play varies too. You might be perfectly fine going as a bassist and playing bass, or you might have to learn another instrument. Again, contacting the schools directly is your best course of action if that is a path you are considering pursuing.
There is a bass specific workshop at Oberlin affiliated with the VSA and many past participants are members of Talkbass, but I am under the impression it is geared towards people already working in the business, not beginners.
That should give you a few options to explore and a couple things to think about.
