apt - How to version control of Kernel ABI versions and matching package repositories?

I need to be able to version control a Ubuntu LTS kernel version at the ABI version level with the matching packages for my current and future installations of a given kernel.

Given the Ubuntu kernel version numbering scheme:

[base kernel version]-[ABI number].[upload number]-[flavour]

Part 1

How long is a given kernel ABI version of the kernel supported for with LTS releases? For example, when creating an Amazon AWS 16.04 image, the kernel is currently 4.4.0-36. In general, how long should I expect the -36 version to remain available? By available I mean I can obtain the image from an official Ubuntu download site and install packages for that OS/kernel version without having to downgrade packages.

Part 2

Assuming I want to be able to support a given ABI level of the Kernel for longer than the ABI version is available on the internet, what do I need to do to mirror the package repositories so I can install packages on my systems? Are there any guides on how to create a local mirror of packages so I can maintain a version controlled OS baseline against a given kernel ABI? I understand that once the kernel has been superseded, it is difficult to take a current image and downgrade it to a desired baseline as the package repository baselines are not archived as such.