You do realise that both the latest Firefox and Chrome require way more memory than the N900 has? I don't think you've understood me yet, Maemo Leste is built on top of Devuan, that means it includes the entire Devuan software library which is almost identical to Debian. The same Firefox, Chrome, Docker and GNOME 3 packages are available in Leste. The kernel is currently missing all of the config options required for full container support. I recently built a kernel based on the Leste kernel with these options enabled. You can find the config here: https://github.com/dderby/n9xx-linux...rx51_defconfig This should make its way into the Leste kernel at some point. The plan is to support Anbox containers, so that might be a better way for you to run WhatsApp, if it doesn't run out of memory that is.
You're building it on the device? Good luck with finishing that sometime this year!
You'll need libcmtspeech to get audio. Not available in Debian or Devuan but I believe it has now been packaged for Leste.
I can't remember which kernel was used when the stable release was cut, it's definitely newer than 3.16 but it's still older than the Leste kernel. Stable means stable, you won't be able to get a new kernel into the stable release. The Maemo Leste image builder is built on top of the Devuan arm-sdk. The Devuan arm-sdk maintainer is also involved in Maemo Leste and was the one who created the Leste image builder. When the next Devuan release is cut, it will most likely use the latest kernel that has already been tested in Leste. Why bother? Forget about Devuan and just use Leste which comes with Linux 4.15.7 plus PVR patches!