Hi @ming
Welcome to the IPFire community.
I believe this is related to 32 bit ARM. That will eventually be stopped. It has already been marked as a legacy release in the secondary architectures section of the download. Somewhere it will be marked as being deprecated and then stopped.
64bit ARM is still being supported - aarch64. Even there the concern is that every new arm system needs to end up having IPFire custom tuned to be able to work. That is not really supportable, when the devs only have a few examples of the hardware and there are so few core devs working on IPFire.
I can provide input on some of your questions.
IPFire has all the drivers that are in the kernel at the release currently running - 5.15.49. Unfortunately, not all hardware suppliers submit their drivers to the Linux Kernel team to be integrated.
https://wiki.ipfire.org/devel/ipfire-2-x/build-howto
Bear in mind that if you are looking at integrating specific drivers into the build then you can not just build them and add them in.
For security of the firewall, all kernel modules are signed in the build and after the build is completed the key is deleted so no one can ever build a module or rootkit against the IPFire kernel. So to add an additional driver you will have to build the whole kernel and add that to your build process.
If you know the specific driver and it is GPL compatible then you can either submit a patch for the addition of the driver.
https://wiki.ipfire.org/devel/submit-patches
https://community.ipfire.org/t/arm-sbc-support-discussion/2650/68
The other alternative is to raise the driver requirement as a bug but that may take some time as there are only a few people capable of dealing with the integration of drivers into IPFire
For your remaining questions other people with more knowledge of arm on IPFire will have to provide answers.