Bootloader

I have a Samsung Galaxy Tab S LTE (SM-T805). When I do "adb recovery" or when I do "power+vol up" it boots into a "revovery" which says

Android system recovery <3e>
LRX22G.T805XXU1B0D1

etc

I would like to know,

1) is this part of the original/stock Samsung firmware/software, or is it something that was downloaded on the tablet by the previous owner? (I bought the tablet second hand)

2) do I need to install another bootloader if I wanted to install another ROM or is this good enough?

3) could someone please tell me how to install another bootloader?

Many thanks