Welcome, lots of good questions
It’s one of the best go to chips, does hf AND lf stuff
The big items to look for are,
Diagnostic card, it’s like a business card with a large antenna in it, out it near a reader and it will blink LF or HF letting you know what system it’s using, so you can plan things in the future
Field detector keychains, these are actually xLED glass tags that are not worthy or safe of implanting but it had the same coils, so it lets you poke around a reader to find the “sweet” spot an implant has the best chance to read, since not all readers are the same and implants have smaller ranges
KBR1 is a plug in reader, that when it reads a chip will spit out it’s uid like you typed it, useful for basic windows login passwords
XACv2 is a relay board that lets you build or retrofit something like a garage door to use your implants
Things blinking under your skin is fun?
There are 2 flavors of led implants, xLED is JUST an led, no chip… only lights up when in a field just like the field detector
The XSIID is a Hf chip that also lights up a led, I use mine for contact sharing, and logging into my computer
The led is useful because it will work like a field detector when your trying to get someone to read your chip, it helps you find the sweet spot, and it’s a nice visual
This is a complicated answer,
Yes, no and depends
In general each chip has a uid, and payload
In the case of the next, it has 2 different chips, so 2 uids etc
Lf uids can be changed, hf uids (usually) are fixed and can’t be changed
I use the analogy of a metal key, the same key can open as many doors as you want to setup to use that key…
And example would be a gym and your work, presumably both have different locks, so the same metal key isn’t going to work at both…
With rfid, you can ADD your key to their system, which would let you use the same key in both systems, assuming it’s all compatible and the right setups
You can also use the payload independently depending on what it is, I use NDEF data (phone recognizable nfc data) on my Xsiid to share a link to a website with all my contacts, and the uid of the chip also unlocks both my computers even though I use 2 different readers… it outputs the uid the same so it’s the same “password”
I could also enroll the same chip somewhere - if they were willing to
This is a bit caveat… a lot of places and people are dumb, ignorant or unwilling to enroll your implant into their system
Lf stuff is easier as you can usually just copy it to the chip
There’s technically a super weird and complicated but cool hack where you can make a uid spit out 2 uids… but it’s not common
You could also buy 1 kit, and just 1 implant, assuming you mean kit as in bundle
That was a info dump, lemme know what doesn’t clink and I can refine 
