What do I need to know about being stationed at Fort Bliss as a 13F?

While you can always go brush up on the the systems that will be delivering fire downrange that you call for (possibly M109A6, MRLS, etc.) or the organization of the unit (get familiar with 1AD, it's DIVARTY, etc.), the important things you could learn before you go would be the normal ones when going to a new unit.

Become familiar with the unit leadership, the command priorities, and culture. If the unit is doing it's job right, and assuming you have orders already, your sponsor should have reached out to you by now. Hit them up with questions about the battle rhythm you'll be falling in on, unit policies and any 'not in the read-ahead' type of information (for example, we're scheduled for a major exercise in January ... we take block leave from X to Y .. etc)

For now, you can hit up the online docs for the base and major unit (I am making an assuming you're going to 1AD). Look at information that other FOs in mechanized units have given and try to gleam some tidbits from them that you're not familiar with .. then read up on those unfamiliar items.

As a SSG, your bosses are going to be more interested into your leadership skills than your technical proficiency (not that those skills aren't important!). Your ability to get your Soldiers to work well together, meet standards and accomplish tasks are what's most important when compared to your individual skills. Again, you still need to maintain them, but the 'bigger picture' is more important in the grand scheme of things.
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* 1AD DIVARTY: https://home.army.mil/bliss/index.php/units-tenants/1st-armored-division/1ad-divarty
* Standards book for 1AD & Fort Bliss: https://home.army.mil/bliss/application/files/5415/9069/2998/Fort_Bliss_Standards_Book_31MAR19.pdf
* DIVDS - The Might behind the Mechanized FO: https://www.dvidshub.net/news/158185/might-behind-mechanized-forward-observer

Well, the upside is that you want have to hump a ruck nearly as often. Downside is that you will spend a lot more time in the Motor Pool.
I went from Light Infantry to Combat Engineer and did all my Engineer time as a Divisional Engineer supporting Mechanized or Armor Units. I think the biggest difference you are going to find is that the Heavy Divisions will have a much wider variety and heavier indirect fire weapons. I've been out for a couple of decades, but the Divisions I supported had MLRS, 105mm, 155mm, 4.2 mortars and still had 8"Guns when I first switched to the Engineers, plus organic Attack Helicopters (Air Force Controllers kept all the fast movers). I would check the unit's MTOE and see what toys they had that I hadn't played with and do some catch up before I hit the unit.
The other thing I will mention is that your battlefield just got a lot bigger. Light units operate on a scale if Kilometers, Mech units operate over square miles of territory. I would advice pulling a copy of FM 71-2 Tank and Mechanized Infantry Battalion Task Force as a good place to start learning the difference.