I don't think anyone can tell you anything about what processor or GPU you'd need because just doing video editing and Photoshop don't mean much. Are you doing multi-4K video streams with heavy effects? Are you working with a lot of layers in Photoshop with 100-megapixel files? Or are you editing 1080p video footage and iPhone photos? There's a big difference in what hardware recommendations go with that.
My general advice, considering the future, is this:
Get the best CPU you can afford. This is the one component you won't be able to upgrade in the future.
Get the minimum RAM Apple will sell you. It's not cost-effective to upgrade your RAM through them, and unless you're terrified of touching computer internals, the RAM upgrade process is pretty fool-proof. You can potentially save quite a bit by doing it yourself and buying from somewhere besides Apple. Don't feel the need to get "Mac-specific RAM" - that's just a marketing ploy with increased prices. Macs are using the same x86 architecture as everyone else, and as long as you've matched the RAM correctly (same as you'd need to do on a PC), "PC RAM" works the exact same.
I'm mixed on whether to recommend for or against Fusion drives, and whether to recommend going with the minimum SSD size. Your system has Thunderbolt 3, which means you can buy a NVME blade and put it into a Thunderbolt 3 enclosure, use it as your primary drive, and have performance that matches and potentially exceeds what the SSDs that Apple would build into your system can do. However, Thunderbolt 3 enclosures are expensive and that probably won't change any time soon. (Even Thunderbolt 2 enclosures are really expensive, despite being "yesterday's tech.") It also represents another device hanging off of a port. What I'd do for myself is to get a 256 GB or 512 GB SSD through Apple for the convenience, with plans to be on the lookout for deals on enclosures and larger SSD blades, and relying more heavily on external storage until then. This depends more on your own comfort levels and how far you want to go being cost-conscious.
GPUs can't be upgraded inside of the computer, itself, but with Thunderbolt 3 you have the option of using external GPUs that can outperform an upgraded-from-Apple GPU. Upgrade it if you need it for the work you're doing now, but I don't know that I'd go for the absolute maxed out option. Instead, plan to go for an eGPU solution in a few years, which will also extend the longevity of your system. Similar to the discussion on using a SSD in a Thunderbolt 3 enclosure, this is slightly kludgy compared with just having everything sitting pretty inside of the computer.
Welcome to the Mac side, and if you have any other questions, feel free to ask.