I have been successful in stripping components and other features out of a windows image using the WinReducer toolkit (cortana, search, real-time system restore, windows defender, edge, hundreds of useless services and programs/apps, telemetry etc.) and injecting (do not run the bat file inside of windows, it will break everything. Get the injectable version as anything that’s not compatable will just be skipped.) Black-Viper command-line scripts upon initial first-boot. Then running the performance script found on this website, manually disabling Update services, selecting ultimate performance using powershell, overclocking by a base 200mhz. Setting boot ratio to 4 cores (using msgconfig from the cmd line) increases the speed dramatically when turning on the pi and booting to windows. Manually reducing the resolution to 720 with scaling lowers the render cost of the igpu then turning off all windows features such as transparency, real time snap (it actually uses mb’s of ram with multiple windows). When finished, ejecting the SD card and inserting it back into the PC, running WinReducer again and seleting Optimize Iso will further reduce the size of the iso and relocate some things in the background (idk what it does, but it seems to save about 20% in space). Reinserting the SD card, using CCleaner to clean all regestry entries, disabling any programs that might start on boot (shouldn’t be any) and finally using the latest arm build of FireFox Nightly, I have a working raspberry pi Windows PC. About 200ish mb/s ram usage on idle, less than 1% CPU usage. Firefox works great. Injecting K-Lite Kodek pack with WinReducer will allow playability of videos from youtube at low quality, 30fps. Using the Arm64 port of VLC and connecting it to firefox, will allow up to 720p video to be played on youtube with minor skipping depending on the actual video quality. 480p is fine.
I will be writing an in-depth guide on how to do all of this in the next few days, when I test this all out a bit more. Until then, please, drop any more optimizations you might have. We aren’t here to play crisis! 
Anything involving deleteing unused services, programs that will never be available on the pi, all of this will help in reducing the load cost. If you can find out how to delet system 32 without it messing up windows, then do it! Haha, jk but seriously, drop any and all tips here!