It's definitely not necessary to have a vitamix, but a powerful blender will make things a lot easier. Generally, I think a blender that is rated ~2+ HorsePower (HP) should suffice. The other consideration is the volume of the container. These days a lot of new vitamixes come with a wide-base 64oz container, which has some advantages but that generally means a higher minimum volume/batch size required. For nut milks it's probably fine as I usually make 32oz+ but the downside is for other applications the high minimum required volume can be frustrating. So with that in mind I think considering the taller profile at the 48 or 64 oz size is worth considering.
Looking at some of my notes from years past I had denoted this rough guideline of ratio of nut to water. You could think of this maybe as a relative ratio in Cups but I think any unit of measurement should work. I tend to lean more toward the creamy-full body zone but you can also yield that by incorporating some other things (macademia nut, coconut butter) which have inherently higher fat content and will increase the body & mouth feel. You will ultimately lose some of the water in the process due to absorption in incomplete straining so I have not really thought about that too much but these are the inputs.
The nuts I like to work with are:
Soaking will yield better milks. Briefly, soaking will make certain nuts easier to blend but also will trigger a germination process where enzymatic inhibitors preventing sprouting will be moved into the soaking water. Though I have not looked too much into it this should also make things more digestible.
Different nuts have different soak times. As a result mixing nuts can sometimes be tricky to find a uniform soak time or handle different soak times. I usually soak room temp in a mason jar. You can over soak nuts and it can result in an off tasting milk. You can compensate for that by moving the soak process to the fridge, or once soaking is complete just refrigerating the nuts without the soak water. Some people will soak nuts and then freeze them and use as needed. I've never done this myself.