No matter what starter you buy or are gifted … ultimately it becomes “your” starter in that it has the bacteria and characteristics of your location and conditions. So, you can buy SF or Seattle or Alaskan starter, but eventually it will be “Your house” starter.
As far as “sourness”, Melissa’s link and searching will get input on making your starter and bread more or less sour.
At my house, in Northwest Montana, with a starter of a local minimally processed flour and my own well water (untreated, so I assume full of GREAT bacteria!), and a weekly/semi-weekly feed and bake … I have not much sour but a flavor I happen to very much like so have not messed with it. Side note: I keep my house VERY cool at 62-65F Fall-Winter-Spring and as close to that as I can get in the Summer (typically 65-68F). Those cool temps “theoretically” are unfriendly to starter and naturally leavened bread and baked goods. Hah! Not so for me