Customize wrt1900acs build with latest kernel and wifi


after using now openwrt and in the latest past Lede I would like to start building custom build with latest kernel and wifi driver for the wrt1900acs (v1).

I have read about how to a couple of month ago but unfortunatelly. I can´t find the post anymore.

Is there anybody so kind to describe a bit in witch files I have to changer the version of kernel and mwlwifi driver and where do I find the latest kernel and driver for the 1900acs?

Thought as well to compile new kernel, but I guess this is a way to advanced yet for my experience.

I am using the acs as well with extroot on a small usb3.0 hard drive. Is there a way to configure and build that this is integrated by default to the image?

About upgrading the packages. I used the developement snapshot in the past. But after a while when I want to install or upgrade a package of course the kernel is out of date and the wnated package can not be installed without reflash to latest image. Is there a way to fully upgrade without need to reinstall the hole settings/ packages?

Thank you!

Kindly regards..