So.
Your final deliverable will be 8 bit.
What ever it is finally viewed on will be 8bit.
Ideally you should have AE as a 32 bit project but the working space should be set to Rec709.
That way you will not be creating saturation that can never be in the final rec709 deliverable
Premiere works in Rec 709 by default. It is faking and fudging it HDR workflows
You don’t need to work in 8 bit AE project, keep it 16 or 32
Your system can handle it fine, just get as much RAM as you can, and maybe get a second NVME drive for cache
Export as Pro Res 4444 as RGB+Alpha and Trillions+ but be aware that this is full range RGB and your final video will probably be video range
You now have 10 bit clips with alpha that Premiere should interpret correctly
PNG are a bit didgy and the gamma gets misinterpreted a lot
Tiffs or EXR can be 32 bit but you don’t really ever need that and your system prtobably can’t play them properly
If you export Pro Res 422HQ Masters from Premiere and use AME to encode deliverables you should be seeing what you want. You should be judging on an extrernal monitor, ideally via decklink.
Be aware the viewer in Premiere is usually wrong.
In a year or so HDR workflows will mature and you will be able to have wider colour gamut RGB video deliverables but at the moment it is far far safer to stick to Rec709.