Threadripper seems a bit overkill for photo editing. I'm not 100% sure, but I think photo editing especially with Adobe is mostly single-threaded (*or at least benefits from faster single-threaded performance.) If you went Threadripper, you probably would gain little or actually lose single-threaded performance over the Ryzen 7 2700X. Ryzen 3000 is coming up soon, so maybe even wait for that. On the other hand, Intel is also very good and is faster at single-threaded tasks, which can include photo editing.
Is there are reason you need the perks of HEDT such as X399 (AMD) or X299 (Intel)? If not, I would recommend Ryzen 7 2700X (or wait for Ryzen 3000) or Intel i9-9900K at the MOST. You can do just as well for casual editing with a Ryzen 5 or Core i5.