Welcome to the site.
Mods all depend on what you want to have your ST look like. Performance, looks, and convenience. Money, time, and tools. oh, and your own ability to work on things of course.
Best way to find stuff is just go down the rabbit hole and GTS (google that stuff).
7K is a great price for a vehicle with 10k miles. There is a 01 ST in the PNW at a dealer with 4600 miles asking 20K.
https://seattle.craigslist.org/est/ctd/d/woodinville-2001-ford-explorer-sport/7824323666.html
and another 04 ST with 88k asking 12k...
A couple of mods...
F150 turn signal mod, worth it to me as a tall person my knee would hit the turn signal when in the left turn and shut off.
Then the rear tailgate handle with camera mod...
before:
after:
Both are worth it.
For my topper, the PO or installer ran the wires through...
It is a 4WD, the AWD selection is a smoother working system that the earlier Auto4X4 system. No clunks when system engages because the AWD portion acts like a limited slip differential inside the t/case. I want to say it's like a 30/70 or 35/65 allowance.
I don't believe the STs came with a rear window defroster. Could be wrong though.
You can add one to the rear window, but if your window rolls up/down it may be difficult. Fixed window just buy a kit and install.
My bad, I forgot yours was IRS. RA has a ton of replacements, I would research each one and find out which one is the stronger.
https://www.rockauto.com/en/catalog/ford,2010,explorer+sport+trac,4.6l+v8,1444730,drivetrain,cv+axle,2288