Ubuntu 14.04 install hardware enablement stack for kernel beyond 3.13.x?

I know there are tons of documents online talking about hardware enablement stack, I also know the theory for LTS to get more closer kernel and X library, so does it means I CAN NOT install kernel beyond 3.13.x on 14.04 LTS platform unless I install HWE stack? I am trying to understand in detail of the steps before execute upgrade on production servers. Also, does HWE stack cause conflict on packages or kernel module?

I also tested install kernel using "apt-get install linux-image-3.19.0-18-generic", it render unbootable system and have to rescue by boot into 3.13.x older kernel and remove it, this cause confusion, if I could see on apt-get, should I be able to install new kernel without making my system unbootable?

You can install kernel 3.16 by running

sudo apt-get install linux-generic-lts-utopic

or kernel 3.19

sudo apt-get install linux-generic-lts-vivid

This will install meta packages and the selected kernel major version will get updates using normal sudo apt-get update && sudo apt-get upgrade routine.

Why did you install an old 3.19.0-18? Current is 3.19.0-23.

I use all my Ubuntu 14.04 systems with kernel 3.19 with no problems.