5.1.1 - double checking my options

I more or less understand the differences between versions and the install process, but I wanted to double check some things..

I just bought a Fire 7 2015 with 5.1.1 on it. I've used SuperTool to root and all its other functions. I want to install a custom ROM. There's detailed information about 5.0.x and 5.1.2+, but 5.1.1 seems like an odd duck.

- What is the difference between 5.1.1 and 5.1.2? Aside from the system, does it have a different bootloader and recovery?

- 5.1..1 doesn't allow modifying the bootloader or recovery, right? Not even temp booting TWRP? So, is the recovery same as 5.1.2?

- So without TWRP, I have to use FlashFire on 5.1.1?

- To revert back to stock FW, I can sideload 5.1.1, right? I don't have to sideload 5.1.2?

- Any comments on a ROM? I've used CM and AOSP before, but never Slim. There is varying information regarding which ROMS can be used on which Fire versions.


TIA.

Root Checking on my tablet

I have Penta T-Pad WS704X 3G calling tablet. It runs on lollipop 5.1.1

The issue is regarding it rooted or not. I haven't root it yet, so I think its rooted by manufacturers. The problem I'm facing is that I have installed ccleaner on it and in system info it says that my tab is rooted, but when check the root by using root cheker app it says my device is not properly rooted.
By checking on terminal I get $ sign, and when typing SU I get permission denied.
And in ES file explorer I can't ON the root explorer which it says "test fails, this function can't performed on this device"
Is my device is rooted or not?

It also have su file in system/xbin and sh and busybox in system/bin by default.
I haven't try any rooting procedure yet.

So question is whether my device is rooted or not by the manufacturers?

Please help, I'm unable to move my apps to SD card.