Make and model of your AIO? You might want to state the specs to your build and parse images of your build to help us understand what the layout of your chassis interior is and how it's setup. Often times people just ask around, we give suggestions and they return with complain that things went South after adding fans. So if you will, we'd need the additional info.
Please list the specs to your build like so:
CPU:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
and you can host your images on Imgur or their ilk and parse the links into this thread for us to see.
If you were starting fresh, I'd have advised on sticking with the fans bundled with said AIO and leave them be. If you want to add more fans, either work with the same fans that were paired with the AIO or replace them all, the latter is expensive but it keeps your cabling, app management and aesthetics coherent.