In terms of hardware, what are some good cost effective resources and what what things might I want to consider differently than what I am used to in both the Mac and Windows worlds? I need smart home management, a plex hub, and photo editing, as well as the usual other stuff.
What are you currently using for smart home? Might be helpful to list in the OP what programs you are used to in general btw. Most smart home systems are managed through the browser but I can imagine Apple’s HomeKit may have some OS level integrations.
Personally, I use Home Assistant, which is an open source home automation hub that can interface with most vendors, including Homekit. This gives you the freedom to buy Apple, IKEA, Philips, Sonoff or other smart home products and use them all through a unified hub that has your automations. But I don’t recommend adding Home Assistant and switching your desktop to Linux at the same time.
Try to change as little as possible and do one thing at a time.
Maybe getting started with learning GIMP is a good first step?