Recommendation for my hardware upgrade. Aspiring but amateur video/photo editor

Unfortunately, you're stuck. Adobe has ceased development and also EOL'd all of its non-subscription software outside of its Elements line several years ago. Thus, the only way up (Adobe-wise) would be something with "Cloud" in its name.

And a misnomer about Creative Cloud: The software does not actually run from the Cloud itself. In fact, all of the program files are stored and run locally inside your own PC. An Internet connection is required at least once every 30 days to verify that your subscription is still valid. That, plus the ability to store your project files in the cloud, are what put "Cloud" in the program's name although you may choose not to store your project or media files in the cloud.

With that in mind, I would not buy an i5-9400 at this point. It has been superceded by Intel itself with the introduction of its replacement, the i5-10400. The new i5-10400 now has 6 cores and 12 threads (versus only 6 threads in the i5-9400). That makes the i5-9400 not sufficiently faster or more powerful than a 3.5-year-old 4-core/8-thread Kaby Lake 7th-Generation i7 CPU to justify its current street price. And Intel almost never reduces the price of its outgoing CPUs when it introduced its new lineup. In fact, Intel tends to keep the prices of its older stuff at full list price until the day they get discontinued.