My take on a HDZero 75mm whoop, flies really well and I'm happy to share my CLI or any tips on how to get the FC mounted on the bottom etc. Most of what I have done is inspired by the work of others and I simply choose the bits I like from each. For my own flying I use my MobThicc V3 build as the benchmark and to be honest this doesnt touch that for flight performance but it has HD which is awesome for obvious but completely different reasons.
Things of note:

1. rotate frame 90 degrees from normal so the battery is toilet tanked and the usb port is accessible
2. Mounting the FC on the bottom side of the frame but still above the battery tray helps with flight performance (I assume by centralizing the mass). The tiny motors and props don't have to work as hard and I found I could push the PID tune a bit more. If you hold the frame up to a light its very easy to see where the existing mounting holes are and start holes from the bottom to line up perfectly. Mr Shutterbug has a great video on how to mount an FC this way, the piece specific to the frame starts at about 12:50 here -> https://youtu.be/hufEk1cLG1c?t=768
3. I personally love high kv on my whoops and use 25k on almost everything and spec props to get what I want out of them. In this case I settled on the Azi triblades because they bring back a bit of the agility lost from adding the extra weight and flight times are right in line with the gemfan biblades which are a fine option too but the quad feels like its sliding in the corners.
4. An upgraded battery connection is noticeable to me on this heavier setup, less sag and more flight time. I like to solder mine up at a 90 deg angle so its clean when plugged in.
5. Depending on what battery you use a tiny elastic to loop over the battery is approaching critical. I stole that idea from Heads at Infinity Loops and battery movement is just not a thing anymore for me no matter what size battery I am using.